President Obama issued two orders yesterday that could ultimately toughen fuel efficiency requirements for new cars and light trucks in what could prove stiff medicine for a U.S. auto industry already hobbled by financial troubles.

With General Motors and Chrysler leaning heavily on billions of dollars of federal loans, Obama is in a strong position to remake the industry with an eye toward cutting U.S. petroleum consumption and greenhouse gas emissions.

"Our goal is not to further burden an already struggling industry," Obama said, but to help American automakers "prepare for the future" and "thrive by building the cars of tomorrow."

The president raised hopes on all sides for a resolution of years of divisive debate over fuel efficiency requirements. Environmentalists and many state officials said they hope that Obama would endorse tough tailpipe emissions standards proposed by California. Automakers, meanwhile, want the administration to establish uniform nationwide mileage standards while moving to ease the cost by providing assistance and incentives for car buyers.

"If you're a stakeholder, you hope the stake goes in ground and not in your back or chest," said David McCurdy, president of the Alliance of Automobile Manufacturers, who watched Obama sign the orders yesterday at the White House.

Flanked by Transportation Secretary Ray LaHood and Environmental Protection Agency Administrator Lisa P. Jackson, Obama directed the EPA to reconsider granting California and other states waivers to set their own strict regulations over tailpipe emissions. California would require a 30 percent cut in those emissions, a mandate more stringent than the federal mileage standards. The new review process could take several months.

Obama also instructed the Transportation Department to draw up new interim targets for mileage standards starting in 2012 that ensure new vehicles reach the 35 mile-a-gallon level set by Congress for 2020. He left intact Bush administration guidelines for 2011 models already being designed.

"The days of Washington dragging its heels are over," Obama said. Saying the nation has arrived at a crossroads, he said: "It will be the policy of my administration to reverse our dependence on foreign oil while building a new energy economy that will create millions of jobs."

Separately, the State Department named Todd Stern the new U.S. envoy on climate change. Stern, a partner in the Washington law firm of Wilmer Cutler Pickering Hale and Dorr and a senior fellow at the Center for American Progress think tank, served as the top White House negotiator on the Kyoto talks on global warming from 1999 to 2001.

Obama's announcement on fuel efficiency standards encouraged state officials who want to institute their own greenhouse gas curbs but faced opposition from the Bush administration. Ian Bowles, Massachusetts secretary of energy and environmental affairs, said his state had encountered "a strong headwind from the federal government" over the past two years. But "to my mind, today's announcement represents a shift in direction that will lead to a significant federal tailwind."

Maryland Gov. Martin O'Malley (D) also applauded Obama's announcement. In 2007, the Maryland General Assembly passed a so-called clean cars law that would set stricter emissions standards for vehicle models hitting the road in 2010. The law would eventually raise average fuel efficiency of cars told in Maryland to 43 miles per gallon.

"In the long run, it's best for American automakers as well," O'Malley said.

Automakers in the past have not seen it that way and have filed at least three lawsuits in different jurisdictions to stop states from setting their own emission standards. "The suits are still there," said Gloria Bergquist, a spokesman for the Alliance of Automobile Manufacturers. But, she added, "We're the first to say we would like to find a better way forward."

Environmental groups argue that controlling tailpipe emissions from vehicles will do much to address climate change. According to the advocacy group Environment America, applying the California standards to the 14 states that have already adopted them will reduce global warming pollution by more than 450 million metric tons by 2020, an amount equal to eliminating all of the pollution from 84.7 million of today's cars for a year.