The state attorneys general also allege that the EPA did not set sufficient standards for the regulation of sulfur dioxide and nitrogen oxides, which power plants also emit.

EPA officials defended their emissions policy and said they "will review all options and make an informed decision on how to proceed," according to a statement.

"EPA's climate protection programs continue to exceed the agency's greenhouse gas emissions goals and are on target to meet the President's 18 percent goal to reduce greenhouse gas intensity by 2012," a spokeswoman said.

The suit was filed in the federal appellate court for Washington, D.C., and is being handled by the office of New York Attorney General Eliot Spitzer. The other nine states are California, Connecticut, Maine, Massachusetts, New Mexico, Oregon, Rhode Island, Vermont and Wisconsin.

The agency said earlier this month it plans to seek public comment this summer on a proposal to change the way regulators oversee pollution from oil refineries and other industrial plants. The proposal itself is expected to be issued in the early summer.

Also expected this summer is a congressionally-mandated report by the nonpartisan National Research Council that will examine the potential impact the disputed power plant air emission rules have on air quality.

Requested by Congress, this report examines the potential effects on air quality of rule changes made by the US Environmental Protection Agency that govern when older power plants and other industrial facilities must upgrade their emissions-control equipment.

But the executive director of a coalition of state and local pollution control officials said the states' suit was an inevitable result of what he called federal inaction on the causes of and solutions to global warming.

"There has been a steady drumbeat that has become louder and louder around the country, and around the world, recognizing that global warming is a very serious problem and needs to be abated quickly," said Bill Becker of the State and Territorial Air Pollution Program Administrators and the Association of Local Air Pollution Control Officials.