The Obama administration is considering establishing national rules for regulating greenhouse gas emissions for automobiles, according to White House officials, a move backed by both auto manufacturers and some environmentalists.

For weeks, administration officials have been meeting with car companies as well as green groups and representatives from California -- which is awaiting word on whether it will receive a federal waiver to regulate greenhouse gas emissions from vehicles -- to try to broker a deal on the issue. On Sunday, Carol M. Browner, assistant to the president for energy and climate, said she and others backed the idea of a single standard for cars and trucks.

"The hope across the administration is that we can have a unified national policy when it comes to cleaner vehicles," Browner said at the Western Governors' Association meeting in Washington.

Yesterday, a White House official, who asked not to be identified because the policy has yet to be finalized, said Browner's comments did not mean the administration was seeking to usurp Congress's role in regulating carbon dioxide and other emissions linked to global warming.

"The administration recognizes that these are hard times for the auto industry, and we are exploring a process to develop a national policy for autos within the context of larger restructuring negotiations," the official said. "The administration is engaged with Congress to pass cap-and-trade legislation, which the president believes is far superior to a regulatory approach using the existing Clean Air Act. If [the Environmental Protection Agency] finds that greenhouse gases endanger health or welfare, the next steps would be taken thoughtfully and with input from all stakeholders."

The administration is already counting on cap-and-trade legislation passing to generate new revenue for the federal government. A senior administration official, speaking on background, suggested cap and trade would be in the budget because Obama campaigned on it. But he did not confirm its inclusion.

"President Obama's decision to include revenue from an auction is the right policy decision and a very important political statement that they are committed to getting a cap on global warming pollution," said Gene Karpinski, president of the League of Conservation Voters.

Meanwhile, several auto industry officials said they backed the idea of a universal fuel-efficiency standard aimed at curbing greenhouse gases, even if it is stricter than the country's current goal of achieving a fleetwide average of 35 miles per gallon by 2020. California's proposed rule would produce a standard of roughly 42 mpg.

Greg Martin, General Motors' Washington spokesman, said automakers and consumers are seeking "certainty and consistency" when it comes to fuel efficiency. "We've been supportive of a strong national standard, rather than having to comply with the burden of a patchwork of standards state by state," he said.

Gloria Bergquist, spokeswoman for the Alliance of Automobile Manufacturers, said her group was encouraged by the administration's recent moves. "We were hoping the Obama administration could come in and hit the refresh button on this debate," she said.