RAVERSE CITY, Mich., Aug. 4 - Automakers remain divided on whether diesel or hybrid cars are the best way to improve fuel efficiency, and the split is often drawn along cultural lines.

All the major manufacturers are developing cleaner diesel engines, hybrids and hydrogen fuel cells. But companies are pushing harder on different technologies to get a leg up in meeting regulations that are becoming tougher around the world, and their views were represented in comments made at a management conference here on Wednesday.

Toyota and Honda first developed hybrid-electric vehicles, in part because they save the most gasoline in the sort of stop-and-start driving that is common in the clogged traffic of densely populated Japan.

In a hybrid like the Toyota Prius, an electric motor takes over for the gas engine at low speeds and stops; energy is also preserved that is usually lost in braking.

But automakers in Europe are skeptical about how profitable hybrids can be and prefer diesel-powered vehicles because they offer car owners an alternative to high taxes on gasoline.

Environmental advocates remain cautious about diesels. Compared with conventional gasoline cars, they offer lower emissions of the kind that contribute to global warming but lag behind in emissions of smog-forming pollutants - though filtration technology is improving. New air-quality rules that will be in effect in the United States by the end of the decade will require diesel and gasoline engines to meet the same emission levels.

On Wednesday, Fujio Cho, Toyota's president, said his company would like to sell 300,000 hybrid electric vehicles next year, which would be about 4 percent of its worldwide production.

"It may be difficult for us to produce that many hybrids by that time, but we have another year to go, so we'll make every effort so we can live up to that goal," Mr. Cho said through an interpreter.

Next year, Toyota will sell three hybrids in the United States: its Prius car and hybrid versions of the Highlander and Lexus RX sport utility vehicles.

"We like to think of it as enlightened self-interest," Mr. Cho said. "If automakers don't reduce smog-forming emissions, greenhouse gases and the need for petroleum, I believe we won't be in business."

His comments came a day after Toyota said it would increase production of the Prius to 15,000 a month from 10,000 by early next year. Most of these will be shipped to the United States, where customers have been waiting six months and longer for the new Prius since its design was overhauled last year.

Tom LaSorda, chief operating officer of the Chrysler division of DaimlerChrysler, which includes Mercedes, said the company was still researching hybrids and had not settled on an offering beyond a small-volume version of its Ram pickup truck to be introduced in the fourth quarter.

"The other one we're really pushing on, and we think will work, is the diesel," he said. "We're starting to see a lot of responsiveness and positive market response from our dealers and customers out there that would like to drive clean diesels in the United States."

Later this year, Chrysler will start selling a diesel version of the Jeep Liberty sport utility vehicle, the first diesel other than a pickup to be offered by one of Detroit's Big Three automakers in a couple of decades.

"We're very fortunate," Mr. LaSorda said, "that we have Mercedes, one of the best diesel technology companies in the world, leading the way here. So we're just tapping into that."

Even the hybrid Ram will use a diesel engine. It will sell in very small numbers - about 100 will be made for businesses and other fleet customers.

Lawrence A. Denton, chief executive of Dura Automotive Systems, a supplier, urged the industry to work harder to improve fuel efficiency, which has stagnated since the mid-1980's amid booming sales of S.U.V.'s and big pickup trucks.

But he also criticized the toughening air-quality regulations.

"We're overpenalizing diesels," Mr. Denton said, adding, "Clearly, diesels are part of the solution, so you can't penalize them and expect to improve mileage."

Environmental advocates disagree.

"That's misleading," said David Friedman, senior analyst at the Union of Concerned Scientists, an environmental advocacy group. "You're not penalizing diesels; they're just put in the mix with all the other vehicles."

"If you want diesels to compete in the marketplace," he said, "they need to compete fairly and meet the same level of emission standards."

Environmental advocates prefer hybrid cars. On Wednesday, the Sierra Club issued a statement praising the Ford Motor Company, which is poised to become the world's first automaker to sell a hybrid sport utility vehicle, a version of its Escape S.U.V. The Sierra Club had previously been a persistent critic of Ford's environmental record.

"The hybrid Escape is a rolling advertisement for better technology and a cleaner environment," said David Hamilton, director of the global warming and energy program at the Sierra Club.

But another group was more critical. "If Ford wants to position itself as an environmental leader," said Jennifer Krill of the Rainforest Action Network, "it needs to do more than produce one improved vehicle in limited quantities."

ETROIT, Aug. 16 - The gap in safety between sport utility vehicles and passenger cars last year was the widest yet recorded, according to new federal traffic data.

People driving or riding in a sport utility vehicle in 2003 were nearly 11 percent more likely to die in an accident than people in cars, the figures show. The government began keeping detailed statistics on the safety of vehicle categories in 1994.

S.U.V.'s continue to gain in popularity, despite safety concerns and the vehicles' lagging fuel economy at a time when gasoline prices are high. For the first seven months of 2004, S.U.V.'s accounted for 27.2 percent of all light-duty vehicle sales, up from 26 percent in the period a year earlier, according to Ward's AutoInfoBank. However, sales growth for the largest sport utility vehicles has stalled lately, while small and medium-size S.U.V.'s, engineered more like cars than pickup trucks, continue to make rapid gains.

New figures from the National Highway Traffic Safety Administration shed light on how wide the differences in safety can be from one vehicle to another in the S.U.V. category, which now encompasses scores of models. For example, a few newer S.U.V. models appear to have a sharply lower risk of rolling over in an accident than other models.

Over all, crash fatalities declined across the board in 2003 to the lowest levels in six years, the government figures show, with 42,643 people killed in traffic accidents in the United States. Much of the decline appeared to come from fewer people driving drunk and more people buckling up. But the United States has not made as much progress as some other developed nations, because rates of seat belt use remain lower here and because of the growing numbers of S.U.V.'s and pickup trucks, which tend to pose greater hazards than cars both to their occupants and to others on the road.

Industry groups have insisted for years that S.U.V.'s are at least as safe as passenger cars, if not safer. One group run by industry lobbyists, called the Sport Utility Vehicle Owners of America, says on its Web site that it is a myth that S.U.V.'s guzzle gas or that their higher rollover rate makes them more dangerous for their occupants. Ron DeFore, a spokesman for the group, cited statistics from the insurance industry, which found last year that fatality rates for newer sport utility vehicles were markedly improved from older models.

"Most people have gotten a skewed vision about the S.U.V. and think they're unsafe, and that's just not true," Mr. DeFore said.

But the main reason for the safety gap in S.U.V. and car fatalities, according to federal regulators, is that S.U.V.'s are more likely to roll over, a particularly deadly accident event that is a symptom of their higher ground clearance.

"It's largely a function of the rollover problem," said Rae Tyson, a spokesman for the traffic agency. "In certain types of crashes, you're more likely to be better off in an S.U.V., but that is offset by the fact the you're more likely to roll over."

Joan Claybrook, president of the consumer advocacy group Public Citizen and a former top auto safety regulator, said, "There's no question that the rollover problem with S.U.V.'s really undermines their safety."

The traffic safety agency reported last week that there were 16.42 deaths of S.U.V. occupants in accidents last year for every 100,000 registered S.U.V.'s. The figure for passenger cars was 14.85 deaths for each 100,000 registered; pickups were slightly higher than cars at 15.17 deaths per 100,000, while vans were lowest at 11.2 occupant deaths for every 100,000 registered.

But not all S.U.V.'s are alike. New government data shows how much better some S.U.V.'s fare than others in tipping situations, the category's weak spot.

This year, the government started conducting rollover tests on a test track rather than merely analyzing the vehicle's dimensions on paper to determine rollover risk, as it had done in the past. One-third of the 2004-model S.U.V.'s that it tested tipped up on two wheels, halting the tests of those vehicles. One S.U.V. made by General Motors, the Saturn Vue, even had its suspension break on both the two- and four-wheel drive models, prompting G.M. to recall the vehicle. No passenger car tipped during the testing.

The traffic agency has also released new rankings of rollover risk for many 2004 models. It calculated that the Honda Pilot S.U.V. has only a 16 percent chance of rolling over during a single-vehicle crash, compared with a 26 percent chance for the Chevrolet Tahoe and for many versions of the Ford Explorer.

The Chrysler Pacifica, an S.U.V. that somewhat resembles a station wagon, was found to have only a 13 to 14 percent risk, comparable to passenger cars, which ranged from an 8 percent risk for the Mazda RX-8 to 15.5 percent for the Subaru Outback wagon.

Rollover risk, though, is only one part of the safety picture. In crashes between vehicles, heavier vehicles tend to perform better than lighter ones, which is one reason that the smallest cars tend to have the highest occupant-fatality rates. The ways that people who own different types of vehicles tend to drive them is also a factor, especially in the case of sports cars.

But weight is not a simple proxy for safety. In a federal crash study this year, large passenger cars and station wagons, averaging about 3,600 pounds unloaded, were found to have a death rate of 3.3 for each billion miles traveled; they were second only to minivans, which had a rate of 2.76.

Ranked third safest after the large-car category were the largest, tanklike sport utility vehicles, which weigh in at an average of 5,100 pounds unloaded; their death rate was 3.79 for every billion miles. Midsize cars, averaging just over 3,000 pounds unloaded, had a 5.26 fatality rate; midsize S.U.V.'s, by far the most popular type, with an average weight over 4,000 pounds, had a death rate of 6.73 in the study.

Even within categories, there was considerable variation in performance from model to model. Detailed results for federal front- and side-impact tests and rollover tests can be found online at www.safercar.gov.

Complicating the safety question is what happens to people in the other vehicle in a collision. Because of the higher ground clearance of sport utilities and large pickup trucks, their bumpers often skip over the crash structures of passenger cars, raising the likelihood that an occupant of the car will be killed or seriously injured.

Automakers have agreed to work together on structural changes, and the traffic safety agency has proposed new rules that would require automakers to install side air bags as a way to mitigate the problem.

he United States, land of gas-guzzling S.U.V.'s and air-conditioned McMansions, might do well to turn to the country some Americans love to hate for lessons on how to curb its reliance on imported oil: France.

Now that oil has reached roughly $50 a barrel and the world is coming to expect relatively high oil prices to last a long time, experts say that a rethinking of America's wasteful ways is once again an urgent undertaking.

And like it or not, France - whose perceived diplomatic obstructionism in the run-up to the Iraq war provoked a boycott of French products by some Americans - has displayed a quality ripe for export: an impressive tenacity in waging what the French call the war on gaspi, short for gaspillage, or waste. It has also done so in a way that the United States has not been able to: over the long term.

Spurred by the oil shocks of the 1970's, France embarked on a vast state-led drive to flush out as much oil from its economy as possible. With the national slogan at the time, "We don't have oil, but we have ideas," it accelerated the shift of electricity production from oil-fired power plants to nuclear reactors, increased taxes on gasoline to the equivalent of $3.75 a gallon, encouraged the sale of diesel-powered cars and gave tax breaks to energy-hungry industries like aluminum, cement and paper to shift from oil to other fuels.

It worked. In contrast to the United States, where oil consumption initially fell but then ended up rising by a total of 16 percent from 1973 to 2003, in France, despite some increase in recent years, oil use is still 10 percent lower today than it was three decades ago, according to the United States Energy Information Administration. (Germany also matched France's record.)

"Americans have completely abandoned their efforts at energy conservation over the past decade and have been incredibly care-free about oil consumption because they believed they would get access to cheap energy - through force if necessary," said Pierre Terzian, an energy specialist who runs the Paris-based consulting firm PetroStrategies.

The contrast between French resolve and American abandon in recent years is sharp. The United States, too, took the high road in the 1970's and early 80's, when the combined impact of the 1973 oil embargo, the growing power of OPEC and the Iranian revolution of 1979 created long gas lines and raised the prospect of an oil producers' stranglehold over the American economy.

The price of Arabian light crude rose from $1.85 a barrel in 1972 to $40 in 1981, or $80 in today's dollars.

Americans responded with a nationwide speed limit of 55 miles an hour, a home-insulating boom and a blossoming of energy-technology start-ups to help businesses cut their energy bills. Vast improvements came in home appliances: refrigerators, for example, now consume a third of the energy needed 30 years ago.

But slowly, the nation resumed old habits. By the late 1980's, with the economy booming and oil prices below $20 a barrel, gas guzzlers were back, cars raced along highways at 75 m.p.h. with impunity and new vehicles' average mileage per gallon, which had almost doubled to 27.5 in 1987 from 14 in 1972, slipped back to 24, compared with Europe's 36.

In the 1990's, the United States, which represents roughly 24 percent of world economic output and an even lower share of industrial production, nonetheless accounted for a third of the growth in demand for global oil.

A big reason for the policy divide, said Amy Jaffe, the associate director of Rice University's energy program, is a cultural contrast of two sharply opposed ways of looking at the world.

"In the United States, we try to control things over which we have no control, like Russia or Saudi Arabia, instead of looking at what we could do inside," Mrs. Jaffe said. "We're like drug addicts. We're looking around for another dealer instead of going to detox."

For now, the presidential candidates are preaching familiar themes in their campaigning, with President Bush calling for more exploration and increased domestic production and Senator John Kerry promoting alternative energies.

But with oil now at $50 a barrel, double what it was two years ago, and with many analysts expecting substantially higher energy prices in the next decade than during the 1990's, some experts are saying that both government and industry are going to need to do some fundamental rethinking of some basic policies.

"The lack of emphasis on demand in the past 20 years in the United States has a lot to do with the predicament we're in now," said Ashok Gupta, an economist with the National Resources Defense Council. "We need to look at what it will take to get manufacturers to offer technologies that people want."

One obvious step, which politicians are loath to even mention, would be to increase taxes on gasoline. Here again, the divergence between the United States and Europe is instructive. To encourage the use of mass-transit systems, and finance their development, European governments impose generally high taxes on gasoline. French drivers pay over $5 a gallon for gasoline, $3.75 of that in taxes, compared with $1.90 a gallon on average in the United States, with only 41 cents of that going to taxes.

Proposing a tenfold increase in taxes to match the European level would, of course, be political suicide in the United States. There have been several attempts to increase federal taxes on gasoline over the years, but "they've all met with disaster," said Kateri Callahan, the president of the Alliance to Save Energy, a business-supported group that promotes energy efficiency.

"Mobility is seen as a national right here in the United States,'' Mrs. Callahan said. "To impose a higher tax when gasoline prices are already perceived to be high is simply not good politics."

At the same time, environmentalists face pressure to accept some trade-offs.

Most European countries, for example, have encouraged drivers to buy cars with diesel engines, which burn 30 percent less fuel than regular engines. Two-thirds of cars registered in France are diesel-fueled, according to the European Automobile Manufacturers' Association. That compares with diesel sales of less than half of 1 percent in the United States.

One hurdle to diesel sales in the United States is that compared with conventional gasoline-powered cars, diesels emit more smog-forming pollutants, though they offer lower emissions of the kind that contribute to global warming. Still, with better technology, some carmakers like Chrysler plan to offer new diesel models later this year.

While diesels have made little headway, fuel-efficient hybrid cars - with electric motors that take over for the gas engines at low speeds and stops - are gaining in popularity. But so far, only a few carmakers offer them, and there is a waiting list for some of the more popular models, like the Toyota Prius.

An additional disparity between the United States and France is the approach to nuclear energy. With domestic production of oil a tiny 3 percent of the two million barrels it consumes each day, France has turned to nuclear power as its economic savior; 80 percent of its electricity now comes from the country's 19 nuclear plants, compared with 40 percent in Sweden, 30 percent in Japan and Germany and 20 percent in the United States.

"Because it didn't draw a lucky geological hand, France has always looked for energy independence," said Dominique Maillard, the country's top official in charge of energy policy as the director of energy at the Ministry of Industry. "We used nuclear power as a path to offset our dependency on imports."

The United States, in contrast, has turned up its nose at nuclear energy, in part because of the risk of a meltdown (much reduced in recent years, experts say), and in part because of the controversy over the disposal of nuclear waste. The biggest factor, though, was the soaring cost of building nuclear plants to satisfy more rigorous standards.

Since the accident at the Three Mile Island nuclear reactor in Pennsylvania in March 1979, no new reactors have been built. With oil prices rising and concern about global warming spreading, nuclear power advocates argue that a new generation of power plants can overcome the problems with nuclear energy at an acceptable cost.

To be sure, the depiction of the United States as the world's energy wastrel and of France as a model of virtue can be overdrawn. All developed countries have significantly improved their energy efficiencies in manufacturing and construction since 1973. Moreover, oil's slice of global energy demand has fallen to 35 percent today from 45 percent 30 years ago.

Still, oil will remain the main source of energy for decades to come, and official projections still show oil consumption in the United States rising by 43 percent by 2025.

But rising prices could go a long way to damp demand.

"The question is, How much do prices have to increase for attitudes to change?" Mr. Gupta of the National Resources Defense Council said.

ETROIT, Nov. 1 - How much will it cost Californians to buy cooler cars?

The Golden State's roads are known for vintage T-birds, customized muscle cars and the Bentleys in Beverly Hills. But the state's regulators have a different kind of cool in mind - cars that emit significantly lower amounts of the gases that have been linked to global warming.

When California adopted the nation's first automotive greenhouse gas regulation in September, the auto industry and state regulators disagreed over how much it would all cost. The new regulation would require a 30 percent reduction, on average, in automotive greenhouse gas emissions - carbon dioxide, nitrous oxide and methane - by the 2016 model year.

The regulation, though directed at greenhouse gases, would probably demand an improvement in fuel economy of more than 40 percent. While smog-forming pollutants have been regulated for decades, catalytic converters can neutralize those emissions. But no filtration technology exists for greenhouse gas emissions, so cutting those emissions would have to come almost entirely from better fuel economy, though a modest amount could be cut by overhauling a car's air-conditioner.

The staff of the California Air Resources Board says the new regulation will add about $1,000 to the cost of an average vehicle, but they said they believed that cost could be made up in five years in savings at the gasoline pump. The industry, by contrast, said it would add $3,000, a cost that would never fully be made up by fuel savings.

If the regulation survives a legal challenge from the auto industry, New York has indicated it wants to follow California's lead. Several other Northeastern states that hew closely to California's air quality standards may also follow suit.

So how would cars and trucks have to change?

The Union of Concerned Scientists, a leading environmental group lobbying for the regulation, recently issued a report on how six specific vehicles could be modified to reduce global warming emissions by 40 percent or more, exceeding the California standards.

The group projected that, for a cost of $1,960 per vehicle, the 2003 model Ford Explorer XLT, with a V-6 engine, could be modified to reduce its greenhouse gas production by 43 percent, a change that would improve fuel economy by more than 70 percent. (California's standards require that emissions from vehicles in the Explorer's weight class be reduced by 24.5 percent by 2016.) The report contends that buyers could make up that added cost in a little over three years by spending less on gasoline.

Thomas C. Austin, the consultant employed by the Alliance of Automobile Manufacturers, an industry lobbying group, to argue against the California regulation, conducted an analysis of the environmental group's projections. (The Ford Motor Company declined to offer its own analysis, referring questions to the alliance.)

Mr. Austin said that according to his analysis it would cost $4,361 a vehicle to make the modifications proposed by the environmental group, and that some changes were not feasible. He also projected a somewhat lower reduction in greenhouse gas emissions. The two sides disagreed about almost every aspect of cost projections because of different methodologies and sources.

"They look for what's been published to support the case to encourage government agencies to further regulate," Mr. Austin said of the Union of Concerned Scientists, noting that to make its case, the group used "the most optimistic projections of fuel economy improvements and the most optimistic projections of cost."

Environmentalists and California regulators argue that the industry's recalcitrance is no surprise, citing its history of opposing everything from safety belts to small increases in fuel economy standards.

"The industry has a long track record of underestimating potential and overestimating cost," said Louise Bedsworth, the senior vehicles analyst at the Union of Concerned Scientists, who wrote the report. "We've seen it on many safety regulations; we continually see this pattern of pushing back, but in most areas we've seen them come through and succeed in the end."

Here are major modifications that Ms. Bedsworth would make to an Explorer to reduce greenhouse gas emissions and Mr. Austin's comments on those proposals.

Aerodynamics

For starters, the Explorer, a sport utility vehicle, would need to be a lot rounder. Ms. Bedsworth said automakers could modestly reduce emissions by improving aerodynamics because cars and trucks that are less wind resistant are more fuel efficient.

"The Explorer is a pretty boxy S.U.V.," she said, a shape that makes it less aerodynamic.

Two current S.U.V.'s, Honda's Acura MDX and the Volvo XC90, made by Ford, are significantly more aerodynamic than the Explorer because of more rounded styling. The company could also cover the underside with paneling to smooth over nooks that hinder wind flow.

Mr. Austin said that Ms. Bedsworth's proposals would make the Explorer an ugly duckling. Some of the most iconic vehicles of the day are characterized by boxiness, from the Hummer to the Chrysler 300C.

"It's been decades since the auto industry showed you could produce vehicles that had half the drag coefficient than vehicles do today," he said. "But look at them. To most people, they're not the kind of cars they want to drive."

Ms. Bedsworth said Ford could also extend the Explorer's steel body over the tops of the tires to improve wind resistance, the way Honda designed the body of its tiny hybrid electric car, the Insight. But Mr. Austin said "most people think the Honda Insight is an ugly car."

Tweaking the Tires

Some new tires improve fuel efficiency with designs and materials that lessen the force needed to propel them down the road. Ms. Bedsworth says she believes further improvements are possible, but Mr. Austin said new federal tire pressure regulations might induce automakers to use larger tires that would impede efficiency gains.

Mike Wischhusen, the director of industry standards and government regulations at Michelin, said changing tire size would not necessarily change fuel economy performance by itself. His company's chief executive, Eduoard Michelin, recently outlined a goal of improving tire performance, as it relates to fuel economy, by 50 percent by 2020.

Under the Hood

Ms. Bedsworth said a variety of technologies could be combined to improve efficiency under the hood. A 42-volt starter generator, a mild form of hybrid technology, would allow the Explorer to shut down at stoplights.

The modified Explorer's engine would also combine three technologies that are in use today, though not all in one vehicle. The altered S.U.V. would have a diesel-like direct-injection gasoline engine that puts air and fuel directly into the engine cylinders rather than into precombustion chambers. The engine would also employ variable valve timing, a technology that ensures that the engine valves open and close in the most efficient manner, and cylinder deactivation, which shuts down one-half of the engine if it's not needed.

Mr. Austin said the last two technologies "don't make engineering sense" when packaged together because they were so similar in nature that using them jointly would not be worthwhile.

Ms. Bedsworth said Honda employed both technologies in its Odyssey minivans, but only one technology - variable valve timing or cylinder deactivation - was used in each minivan, depending on the version.

Ms. Bedsworth said there would still be some added benefit to using both. "The package still comes out to be cost effective," she said.

Increased engine efficiency would slightly increase, to 230 from 210, the horsepower of the 2003 model Explorer used in the study.

Improved Air-Conditioning

The industry is almost certain to argue in its legal challenge that the California regulation is pre-empted by Washington's authority to regulate fuel economy. But environmentalists point out that tweaking a vehicle's air-conditioning system is one way to get modest emissions reductions independent of fuel economy improvements.

The refrigerant used in automobile air-conditioners, known as HFC-134a, is a heat-trapping gas that is even more damaging than carbon dioxide. An improved air-conditioner could contain the gas better, or alternatively, a different type of refrigerant could be used.

Weight Loss?

Mr. Austin said to achieve the kind of emissions reductions proposed by the Union of Concerned Scientists, or the lesser reductions required by the California regulation, the Explorer would have to be significantly lighter. "Our analysis indicates that weight reduction is a more cost-effective way to improve fuel economy than some of the other measures that would otherwise be required," Mr. Austin said.

The use of lightweight materials like aluminum, and the cost of redesign, would add more than $1,000 to the vehicle cost, he said. But Ms. Bedsworth disagreed, saying that the Explorer's weight would not have to change to meet the emissions standards.

Savings at the Gas Pump

Mr. Austin disagreed with projections used by California regulators to gauge how many miles the average vehicle in the state is in service. Those projections are critical to making a cost-benefit analysis of the new standard. He also disputed the discount rate the Union of Concerned Scientists used to calculate the current value of future fuel savings.

Ms. Bedsworth said her projections were conservative, pointing to the $1.68-a-gallon gas price used in her analysis. Gasoline costs $2.39 a gallon, on average, in California, according to the most recent estimate from the Energy Information Administration.

ETROIT, Dec. 8 - Fran Pavley, a soft-spoken, retired schoolteacher who went into California politics, probably never thought she would find herself defending the environmental credentials of Gov. Arnold Schwarzenegger.

But these days, she has been a driving force behind a new battle against global warming. Last month, Ms. Pavley, a Democratic assemblywoman from Agoura Hills, visited Ottawa to seek Canada's help in pressing automakers to cut greenhouse gas emissions. There was some skepticism from the press. As one local journalist put it, "Doesn't your governor drive a Hummer?"

Yes, Ms. Pavley gamely explained, but she was there with the Schwarzenegger administration's support, and the governor had even recently requested and received a special hydrogen-fueled Hummer built by General Motors. By the end of her visit, two top government ministers said they were poised to adopt their own tough plan.

It is safe to say Ms. Pavley, who drives a fuel-efficient Toyota Prius, has the auto industry's attention.

On Tuesday, automakers sued to block legislation she sponsored that would require a roughly 30 percent cut in greenhouse gas emissions from cars and trucks sold in California by the 2016 model year.

"It's the most challenging regulation that's ever been proposed," Thomas C. Austin, a top industry consultant, said in describing its impact on the auto industry. Last month, Robert A. Lutz, General Motors' vice chairman, bemoaned the notion of a single state's trying to regulate global warming, a theory he has doubts about.

"What are they going to do," he said, "put a bubble over California?"

But Ms. Pavley, 55, says that California, as one of the world's largest auto markets, has an obligation to lead the way in North America.

"Almost all nations, with the exception of ours are fully committed to reducing the impact and understand the consequences of not doing so," she said.

After 28 years in education, most recently teaching American history to eighth graders, Ms. Pavley said the linkage of climate change to worsening smog and increased rates of asthma was most troubling to her among a number of potential complications of global warming.

"It's just critically important to California and the Central Valley and all the kids, with asthma skyrocketing," she said, mentioning the San Joaquin Valley, which is the state's prime agricultural region.

Environmentalists see Ms. Pavley's legislation as the only current hope for curbing automotive greenhouse gas emissions in the United States, and by extension, reducing American oil consumption. The Bush administration has declined to join most other industrialized nations in adopting the Kyoto agreement on reducing global warming emissions.

It is also in the early stages of rewriting fuel economy rules for sport utility vehicles and pickup trucks in a way that it has acknowledged could actually increase oil consumption and make trucks less efficient. "We're looking to state and other friendly jurisdictions to move the ball forward," said Daniel Becker, the director of the Sierra Club's global warming program in Washington.

The Pavley plan could put several states on a much different course from Washington. California has the unique authority to set its own air quality standards because they predated the federal Clean Air Act. Other states have discretion to choose California's air rules over those of Washington. As if the industry was not aghast enough at the nation's largest auto market adopting such a regulation, seven Northeastern states are following California and are likely to adopt the Pavley plan. And then there's Canada.

"The potential market force of Canada combining with California and the seven New England states," Ms. Pavley said, "that would be 30 percent of the automobile market in Canada and the U.S. combined."

Pressure from so many regions, she said in an interview shortly before the industry filed suit this week, might "convince the automobile manufacturers to work with us, to send in their engineers and not their lawyers."

For now, it's the lawyers. Greenhouse gas emissions from cars are largely a byproduct of their fuel economy, so regulating emissions like carbon dioxide would indirectly require automakers to improve fuel efficiency significantly. Since the federal government has sole authority to regulate fuel economy, Toyota, G.M. and several other automakers contend in their lawsuit that California is stepping on Washington's turf.

"It's pre-empted by federal law," said Eron Shosteck, a spokesman for the Alliance of Automobile Manufacturers, a lobbying group which filed the suit. "It's something that needs to be done at the national or international level."

California lawmakers say the regulation is focused on harmful emissions and is well within the state's authority.

"We have the legal ability to do this under the Clean Air Act," Ms. Pavley said.

Environmental groups say the regulation can be met with technology already available and not even as complex as the kinds of hybrid electric vehicles made by Toyota, Honda and Ford.

Automakers say they will have to stop selling some of their largest sport utility vehicles in the state. Domestic automakers rely on big truck sales and could be particularly vulnerable. Industry experts say the regulation will add about $3,000 to the upfront cost of the average car or truck. State regulators say it will cost far less, about $1,000, and be more than made up for over time by spending less at gas stations.

Stéphane Dion, the Canadian environmental minister, said soon after his recent meeting with Ms. Pavley that the Big Three automakers, which have a substantial presence in Canada, were not helping themselves by letting Asian competitors lead innovation.

"The company taking the most market now is Toyota," he said, "so I think it's an indication that it's the first movers who are winning in this world."

Ms. Pavley's interest in politics blossomed during a 15-year tenure as the part-time mayor of Agoura Hills, a small suburb west of Los Angeles in the foothills of the Santa Monica Mountains; her assembly district includes well-known Malibu residents like Barbra Streisand and Tom Hanks. Three weeks into her first term in 2001, she was approached by a small environmental group, Bluewater Network, which drafted the bill and was shopping for a sponsor.

"We couldn't get anyone else," said Russell Long, the group's executive director. "I don't think she had any idea of the controversy and the high visibility this bill would engender."

Ms. Pavley, who has a master's degree in environmental planning, concurs. Auto dealers and lobbying groups campaigned against it and ran print ads and radio spots claiming it would lead to higher gas taxes, lower speed limits and fees on gas guzzlers - all proposals prohibited in the final language of the legislation. Two Los Angeles disc jockeys even led a caravan of S.U.V. drivers to Sacramento and heckled government officials outside their offices with a megaphone.

"They would jam phone lines in the offices with all their listeners," Ms. Pavley said. "They could generate a couple hundred phone calls an hour."

The legislation, which passed in 2002 and was signed by Mr. Schwarzenegger's Democratic predecessor, Gray Davis, has the backing of the current governor, who has been shoring up his environmental credentials. The final details of the regulation were approved in September by the California Air Resources Board, which is appointed by the governor.

"He hopes the car companies will see the light," said Terry Tamminen, California's cabinet secretary and a top adviser to the governor, in an interview last week. Mr. Tamminen is also a friend of Ms. Pavley's and was a co-host of one of her first political fund-raisers.

"She has really tried to keep the temperature down, even though automakers and car dealers have been a little hysterical about the potential outcomes," he said. "She tries to be respectful, but like a good schoolteacher, she doesn't hesitate to correct people's misimpressions."