WASHINGTON – The Environmental Protection Agency intends to require that power plants, refineries and other major sources of global-warming pollution get permits beginning in 2011 that would require them to cut emissions, the agency's leader said Wednesday.

In the absence of legislation, the EPA has begun considering ways to regulate stationary sources of carbon dioxide and other greenhouse gases. Businesses say such rules would add new costs and pinch many industries in Texas, the leading source of global-warming pollution among states.

Texas state officials, including Gov. Rick Perry and the Texas Commission on Environmental Quality, have challenged the scientific justification for greenhouse gas controls, arguing that climate change science has been politicized. Under the Clean Air Act, Texas would be required to enforce new rules aimed at lowering greenhouse gases – or risk losing its authority to award all federal pollution permits.

EPA Administrator Lisa Jackson said Wednesday that the EPA would begin by regulating sources that emit more than 75,000 tons a year of carbon dioxide-equivalent gases in 2011 and 2012. That threshold would cover sources such as coal-fired power plants in Texas, as well as refineries, cement kilns and chemical plants.

No permits would be needed in 2010, Jackson said. The EPA wouldn't require permits for smaller sources until 2016 at the earliest, and the threshold for a permit may be set at 50,000 tons instead of the EPA's original proposal of 25,000 tons, she said.

"It will probably be at least two years before we would look at something like a 50,000 [ton] threshold," Jackson told a Senate Appropriations subcommittee on Wednesday.

The details of how the EPA intends to regulate greenhouse gas emitters remains the subject of speculation among lobbyists, environmental groups and industry lawyers.

The EPA's proposal, announced in September, would use an existing program to require that newly built and modified sources use the best available technology to limit greenhouse gas emissions. Whether the agency can use a separate program to cover all other existing major sources is a more nettlesome question that would probably be litigated.

"The question of whether and how existing, on-the-ground stationary sources will be regulated is open," Nathan Richardson, a visiting scholar at environmental think tank Resources for the Future, said Wednesday at a seminar in Washington.

The House passed legislation last year to create a cap-and-trade system, which would allow businesses to buy and sell pollution allowances to meet emission reduction targets. But that concept has stalled in the Senate.

In the meantime, Republican lawmakers including Rep. Joe Barton of Arlington are pushing resolutions that, if approved, would invalidate the EPA's basis for regulating greenhouse gases.

Jackson told senators that the Obama administration still prefers legislation to limit carbon pollution. But some environmental groups and industry lawyers say the agency could create a limited cap-and-trade system even without congressional approval.

"The question is how aggressively that authority can be used," Jeff Holmstead, a former EPA official and partner at Bracewell & Giuiliani, said at Wednesday's seminar.

"Something like the 5 to 10 percent reductions ... can be accomplished under [the Clean Air Act] as long as there is a showing that existing technology can be used to get those reductions," Holmstead said.