WASHINGTON -- The Supreme Court appeared deeply skeptical yesterday about allowing states to sue electric utilities to force cuts in greenhouse gas emissions from power plants.

Both conservative and liberal justices questioned whether a federal judge could deal with the complex issue of global warming, a topic they suggested is better left to Congress and the Environmental Protection Agency.

The court heard arguments over whether to end the lawsuit by six states, New York City and three conservation groups against four private companies and the federal Tennessee Valley Authority, the nation's five largest emitters of carbon dioxide.

The Obama administration has joined with the companies in asking the high court to throw out the lawsuit. The administration says the EPA already is considering setting emission standards that would accomplish what the states are seeking.

Why let the lawsuit go forward when "the agency is engaged in it right now?" asked Justice Ruth Bader Ginsburg.

The lawyer representing the states acknowledged that the case was before the high court at a "peculiar moment," but said the court should block the lawsuit only if the EPA actually issues regulations.

No statute or rule "currently regulates the emissions of existing power plants," said Barbara Underwood, the New York solicitor general. Underwood said the plants operated by the companies and the TVA account for 10 percent of all carbon dioxide emitted annually in the United States.

"This court should not close the courthouse door at the outset," Underwood said.

Lawyers for the companies and the administration focused on the enormity of the climate change issue to argue against the lawsuit.

"You have never heard a case like this before," said Neal Katyal, the acting U.S. solicitor general. The term global warming, Katyal said, "tells you all you need to know."

The case is the second climate change dispute at the court in four years. In 2007, the court declared that carbon dioxide and other greenhouse gases are air pollutants under the Clean Air Act. By a 5-4 vote, the justices said the EPA has the authority to regulate those emissions from new cars and trucks under that landmark law. The same reasoning applies to power plants.

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