The government made clear on Thursday it will not be rushed into deciding whether to regulate emissions linked to global warming, as the Supreme Court directed nearly a year ago.

Such action "could affect many (emission) sources beyond just cars and trucks" and needs to be examined broadly as to other impacts, the head of the Environmental Protection Agency wrote lawmakers.

Stephen Johnson said he has decided to begin the process by seeking public comment on the implications of regulating carbon dioxide, a leading greenhouse gas, on other agency rules that cover everything from power plants and factories to schools and small businesses.

That process could take months and led some of his critics to suggest he was shunting the sensitive issue to the next administration.

"This is the latest quack from a lame-duck EPA intent on running out the clock ... without doing a thing to combat global warming," said Rep. Edward Markey, D-Mass. He is chairman of the House Select Committee on Energy Independence and Global Warming.

The Supreme Court said in April 2007 that carbon dioxide from burning fossil fuels is a pollutant subject to the Clean Air Act. The court directed the EPA to determine if CO2 emissions, linked to global warming, endanger public health and welfare.

If that is the case, the court said, the EPA must regulate the emissions.

The ruling, in a lawsuit by Massachusetts against the EPA, dealt only with pollution from cars and trucks.

Johnson said Thursday that if CO2 is found to endangered public health and welfare, the agency probably would have to curtail such emissions from other sources as well. That could affect a range of air pollution, from cement factories, refineries and power plants to cars, aircraft, schools and off-road vehicles.

"Rather than rushing to judgment on a single issue, this approach allows us to examine all the potential effects of a decision with the benefit of the public insight," Johnson wrote the leaders of the House and Senate environment committees.

Sen. Barbara Boxer, who heads the Senate Environment and Public Works Committee, noted that Johnson has had nearly a year to respond to the court but "now, instead of action, we get more foot-dragging."

"Time is not on our side when it comes to avoiding dangerous climate change. This letter makes it clear that Mr. Johnson and the Bush administration are not on our side, either," Boxer, D-Calif., said in a statement.

Senior EPA employees have told congressional investigators in the House about a tentative finding from early December that CO2 posed a danger because of its climate impact. They said a draft regulation was distributed to the Transportation Department and the White House.

The EPA officials, in interviews with the House Oversight and Government Reform Committee, said those findings were put on hold abruptly. Johnson has said that enacting tougher automobile mileage requirements in December meant that the issue had to be re-examined.

Johnson said a requirement for greater use of renewable fuels such as ethanol changed the landscape when it comes to CO2 regulation.

"It does not change EPA's obligation to provide a response to the Supreme Court decision," Johnson wrote Congress.

Environmentalists said Johnson's approach seemed to signal no meaningful action on climate change.

"EPA has offered a laundry list of reasons not to regulate," said Vickie Patton, a lawyer for Environmental Defense.

Frank O'Donnell, president of Clean Air Watch, an advocacy group, added, "This means any real action is going to come in the next administration."

But lawyer Chet Thompson, a former EPA deputy general counsel, said Johnson's approach was "very responsible given the numerous issues raised" and ramifications of regulating carbon dioxide.