State officials in Connecticut, Maine and Massachusetts said the suit, filed in Federal District Court in Hartford, is the first time that any state has sued the government to compel action on climate change.

	Advertisement

If the suit succeeds, the E.P.A. will be required to classify carbon dioxide as a "criteria pollutant," under the Federal Clean Air Act, and that would trigger, the state's lawyers say, a process of setting standards for allowable levels in the atmosphere, as the federal government now does for ozone, lead and sulfur dioxide and other gasses.

"Global warming is no longer some abstract threat — it's real and it's urgent," said Richard Blumenthal, attorney general of Connecticut. "Our lawsuit is a last resort."

An E.P.A. spokesman, David Deegan, said the agency was still studying the suit and would have no specific comment. But he said that President Bush and Christie Whitman, the E.P.A. administrator, had made their positions clear.

"The president and Administrator Whitman have said that carbon dioxide shouldn't be regulated as a pollutant; the science on it is more complex, and the answers are elusive right now," he said. "They support a flexible approach that will adjust for new information and technology."

Ms. Whitman resigned last month and is leaving her post at the end of this month. The White House has not yet nominated a successor.

The heart of the states' argument, legal experts said, comes down, to a certain extent, to semantics: what exactly constitutes a pollutant? When the Clean Air Act was passed in the 1970's, air pollution meant things would make people demonstrably sick. But as evidence of indirect consequences has grown — like the chemical combinations that form smog, for instance, or acid rain, which mainly affects aquatic life — the boundary of what is considered harmful has expanded.

The suit contends that while carbon dioxide does not pose a direct threat to human health, it has passed over the threshold of harm because of its role in global warming. The scientific evidence about the buildup of so-called greenhouse gases like carbon dioxide — and the long-term threats posed by climate upheaval on everything from emerging diseases to economics — are so firmly established, the states say, that the government has a responsibility to act.

"E.P.A. itself predicts that the problems associated with atmospheric warming will intensify in the years to come," said Steven Rowe, Maine's attorney general. "The agency has a legal duty to act now."

A spokesman for the Edison Electric Institute, a trade group that represents shareholder-owned electricity companies, said the suit, if it succeeds, would hurt the economy without achieving its desired results. Electric power plants and automobiles account for a majority of the carbon dioxide emissions in the nation.

The spokesman, Dan Riedinger, said there is currently no technological means of eliminating carbon dioxide from a power plant's smokestacks. Imposing atmospheric standards, he said, would force plants to switch from burning coal, which produces lots of carbon dioxide, to natural gas, which produces less. But that kind of shift, he said, could bring havoc to the nation's natural gas supply and delivery system.

"To be effective, any policy response to global warming must allow time for new technology," he said.

Many states are starting to address climate change concerns. This year, Gov. George E. Pataki of New York said he hoped to create a regional consortium of states, from Maine to Maryland, to work on the issue. New Hampshire has passed legislation regulating power plant emissions. California passed a law last year requiring reductions in carbon dioxide for automobiles.

"There's a lot of activity, and it's all building," said Ashok Gupta, the director of air and energy programs at the Natural Resources Defense Council, a New York-based conservation group. "At some point, we will be regulating carbon dioxide at power plants, if not in the whole economy. It's a question of when."

Copyright 2003 The New York Times Company