The EPA took a first step on Friday toward federal regulation of greenhouse gas emissions, a move that will put pressure on Congress to address the issue through legislation.

The agency issued a “proposed endangerment finding” that says carbon dioxide and five other gases threaten public health and welfare by triggering global climate change. The document also says emissions from motor vehicles are contributors to global warming.

The EPA is responding to a 2007 Supreme Court decision that found greenhouse gases are pollutants and directed the agency to determine if they threaten the public. The agency will now consider regulations for motor vehicle emissions and possibly electric power plants under the Clean Air Act (PL 101-549).

President Obama has asked Congress to cap greenhouse gases from vehicles, power plants and industry, and set up a market-based program for businesses to meet the cap. The EPA’s finding amounts to an implicit threat that if Congress does not act, the Obama administration could move to regulate emissions under the current law — an approach which could prove more cumbersome and expensive.

An EPA news release stated that Obama and agency Administrator Lisa P. Jackson have “repeatedly indicated their preference for comprehensive legislation to address this issue and create the framework for a clean energy economy.”

Sen. Barbara Boxer , D-Calif., chairwoman of the Environment and Public Works Committee, said in a statement that the changes are “long overdue” but legislation is the better approach.

“The best and most flexible way to deal with this serious problem is to enact a market based cap-and-trade system which will help us make the transition to clean energy and will bring us innovation and strong economic growth,” Boxer said.

Committee ranking Republican James M. Inhofe of Oklahoma, the Senate’s leading skeptic on global warming, issued a statement saying that neither approach would work.

“It’s worth noting that the solution to this ‘glorious mess’ is not for Congress to pass cap-and-trade legislation, which replaces one very bad approach with another,” Inhofe said. “Congress should pass a simple, narrowly-targeted bill that stops EPA in its tracks.”

Hill Action

The House Energy and Commerce Committee is scheduled to begin marking up legislation by Chairman Henry A. Waxman , D-Calif., and Edward J. Markey , D-Mass., during the week of April 27.

Markey, who chairs the subcommittee on Energy and Environment, will hold hearings next week with nearly 80 witnesses, including Jackson, Energy Secretary Steven Chu and Transportation Secretary Ray LaHood . The hearings will begin April 21 with opening statements from members and continue until April 24.

The draft House bill would limit greenhouse gas emissions, but also preempt the EPA from regulating them under several existing standards that apply to conventional pollutants, such as smog and soot.