The delays come as the president is reaching out to a newly empowered Republican Party on tax policy, a move that is angering his own Democratic base. He must now decide whether to make similar efforts on environmental issues.

“Obama has already signaled that in his quest for re-election he’s more than willing to turn against his base in order to make a compromise with his adversaries,” Frank O’Donnell, president of Clean Air Watch, an advocacy group, said in an e-mail, responding to the rules delay.

Mr. O’Donnell said the administration was clearly “running scared” from the incoming Congress and said he suspected that it was willing to moderate its stand on a variety of environmental regulations, including pending greenhouse gas rules aimed at reducing the pollutants that contribute to global warming.

The E.P.A. has said that it will begin regulating carbon emissions from power plants and other major stationary sources on Jan. 2, as a prelude to broader regulation of carbon dioxide in future years. Delaying that program would undercut much of what officials are trying to do in international negotiations like the United Nations climate talks now under way in Cancún, Mexico.

“Look, in January there will be appropriations battles and a whole lot of other tough fights,” said Jeffrey Holmstead, head of the E.P.A.’s air quality office in the recent Bush administration and now a lobbyist for industry. “The administration is going to be feeling a lot of pressure, and they would be better off to do some sort of a deal acceptable to the Republicans to delay this rather than having to threaten a veto.”

The delayed smog rule would lower the allowable concentration of airborne ozone to 60 to 70 parts per billion from the current level of 75 parts per billion, putting several hundred cities in violation of air pollution standards. The agency says that the new rule would save thousands of lives per year but cost businesses and municipalities as much as $90 billion annually.

The boiler rule would affect 200,000 industrial boilers, heaters and solid waste incinerators and is intended to cut emissions of mercury and other dangerous pollutants in half.