Mr. Obama's presidential memorandum will order the EPA to reconsider the Bush administration's past rejection of the California application. While it stops short of flatly ordering the Bush decision reversed, the agency's regulators are now widely expected to do so after completing a formal review process.

Once they act, automobile manufacturers will quickly have to retool to begin producing and selling cars and trucks that get higher mileage than the national standard, and on a faster phase-in schedule. The auto companies have lobbied hard against the regulations and challenged them in court.

In addition, Mr. Obama will direct the Transportation Department to quickly finalize interim nationwide regulations requiring the automobile industry to increase fuel efficiency standards to comply with a 2007 law, rules that the Bush administration decided at the last minute not to issue.

To avoid losing another year, Mr. Obama will order temporary regulations to be completed by March so automakers have enough time to retool for vehicles sold in 2011. Final standards for later years will be determined by a separate process that under Mr. Obama's order must take into consideration legal, scientific and technological factors. He will also order federal departments and agencies to find new ways to save energy and be more environmentally friendly. And he will highlight the elements in his $825 billion economic stimulusplan intended to create jobs around renewable energy.

But the centerpiece of the anticipated announcement is Mr. Obama's directive to the Environmental Protection Agency to begin work immediately on granting California a waiver, under the Clean Air Act, which allows the state, a longtime leader in air quality matters, to set standards for automobile emissions stricter than the national rules.

By JOHN M. BRODER and PETER BAKER from the New York Times