April 14 (Bloomberg) -- Vehicle emissions probably will be the first target under a proposed U.S. finding that greenhouse gases pose a health danger, with decisions on power plants and other polluters coming later, environmental groups said.

“There is a strong anticipation that the endangerment finding, if and when it’s made, will focus on the contributions of motor vehicles,” said David Doniger, policy director of the climate center for the Natural Resources Defense Council, on a conference call with reporters today.

The White House completed its review of the Environmental Protection Agency’s proposal yesterday, said Kenneth Baer, communications director at the Office of Management and Budget. “The proposed finding has been returned to the EPA for further action as the agency deems appropriate,” he said.

If made final, such a finding would clear the way for the EPA to impose the first limits on carbon dioxide emissions from carmakers such as General Motors Corp., utilities such as American Electric Power Co., along with steelmakers and other manufacturers.

The 2007 Supreme Court ruling that required the U.S. to reconsider whether greenhouse gases are a pollutant that should be regulated under the Clean Air Act concerned new cars and trucks.

Still, if a finding is made that greenhouse gases pose a danger, the Clean Air Act gives the EPA authority to limit the emissions from many sources, including power plants and steel mills, said David Bookbinder, chief climate council for the environmentalist Sierra Club.

“EPA will have to make separate decisions about all the other sources,” he said on the conference call ahead of an EPA announcement, which environmentalists have said they expect this month.

Pressure on Congress

A so-called endangerment finding by the EPA would also ratchet up pressure on Congress to pass new limits on emissions from coal-fired power plants and factories, rather than allowing the EPA to develop all the rules for industrial polluters.

President Barack Obama, business and environmental groups say they prefer that Congress develop laws so that competing interests would have a say.

Democratic Representatives Henry Waxman of California and Edward Markey of Massachusetts have offered draft legislation that would reduce greenhouse-gas emissions, which some scientists say cause global warming, 20 percent by 2020 and 83 percent from 2005 levels percent by 2050. Hearings are scheduled to begin next week.

Before a proposed EPA finding becomes final, there is a period of public comment. The document the EPA submitted for White House review doesn’t propose requirements on greenhouse gas emitters or new regulations on current projects, EPA spokeswoman Adora Andy said last month.

The regulatory process is set up for “maximum citizen participation,” Baer said. If regulations follow, they will not come for “quite some time, as this is very early in the process,’” he said.

To contact the reporter on this story: Catherine Dodge in Washington, at cdodge1@bloomberg.net.

Last Updated: April 14, 2009 14:08 EDT