The agency "has a huge role to play in continuing the work to move from where we are now to lower carbon emissions", said the official, who did not want to be identified as the EPA policies are still being formed.

President Barack Obama, looking to take the lead in global talks on greenhouse gas emissions, has long warned that the EPA would take steps to regulate emissions if Congress failed to pass a climate bill.

The Senate has all but ruled out moving on greenhouse gases this year, even though the House of Representatives passed a bill last year. In late July, Senate Majority Leader Harry Reid stripped climate provisions out of an energy bill, saying he could not get one Republican vote for them.

The senior official stopped short of saying the EPA alone would achieve Obama's goal of about 17 percent reductions in greenhouse gases by 2020 from 2005 levels.

"With legislation you almost certainly get more emissions reductions than you get with existing authorities" that the EPA can use under the Clean Air Act, the official said.

And analysts say the EPA will not be able to achieve the far deeper cuts needed to help prevent the worst effects of climate change such as floods, droughts and heatwaves.

Though Congress will not likely move in 2010, the EPA expects it will do so in coming years, the official said.

EPA plans on smokestack emissions face obstacles in Congress and in the courts. Senator Jay Rockefeller, a West Virginia Democrat, and other lawmakers hope to stop the EPA from regulating the emissions for two years.

Energy companies -- from wind and solar power makers to utilities -- are concerned about the regulatory uncertainties, with some analysts saying billions of dollars of investments are stymied by the lack of direction in Washington.

The official said the EPA rules would provide regulatory certainty that could help businesses get loans to build new plants. A two-year delay would only prolong the uncertainty, and hurt the chances of getting financing, the official said.

NEW RULES

The EPA has worked with the Department of Transportation to set new fuel-efficiency standards, as well as the first greenhouse gas emissions rules, on cars and light trucks. More standards for vehicles sold after 2017 are expected to be released later this month.

The EPA also has moved to regulate greenhouse gases from stationary sources such as power plants and factories.

Starting next year the EPA will require large power plants, manufacturers and oil refiners to get permits for releasing greenhouse gas emissions, though details are unclear.

The EPA will also require industrial sources to submit analyses on the so-called "best available technology" they could add to their plants to cut emissions under the existing Clean Air Act.

The official said the EPA will put out guidance this month that would help companies determine which technologies -- perhaps moving to cleaner-burning natural gas and away from coal -- would make the most sense.

In addition, the EPA is working on rules to cut emissions of mercury from coal-burning power plants and cement plants and on toughening rules on coal ash. In combination, the rules could help force inefficient coal plants into early retirement.

That could hit shares in big coal burners such as American Electric Power and Southern Co..

A recent Bernstein Research report said upcoming EPA rules could push 15 percent of current coal-fired power plant capacity into early retirement by 2015.

The EPA will soon roll out more regulations on greenhouse gases and traditional pollutants like mercury emissions that will help cut planet-warming pollution and emissions that more directly hurt human health, the official said.

EPA Administrator Lisa Jackson plans to attend a meeting in Mexico in October aimed at reducing emissions of methane, a greenhouse gas about 20 times more potent than carbon dioxide, the official said.

The meeting will come a month before representatives from rich and developing countries convene for annual U.N. climate talks in Cancun, Mexico.

(Editing by Walter Bagley and Dale Hudson)