WASHINGTON – The Supreme Court entered the debate over global warming Monday, agreeing at the urging of environmentalists to rule on whether new cars, trucks and power plants must be further regulated to slow climate change.

The court’s action gave a surprising, if tentative, victory to 12 “blue states” and a coalition of environmentalists who say the federal government must restrict the exhaust fumes that contribute to global warming.

Their appeal accused the Environmental Protection Agency of having “squandered nearly a decade” by failing to act.

The court voted to take up the issue over the objection of the Bush administration. Its lawyers questioned whether the government can and should “embark on the extraordinarily complex and scientifically uncertain task of addressing the global issue of greenhouse gas emissions” by regulating motor vehicles sold in the United States.

The case, to be heard in the fall, could be one of the most important environmental disputes ever to come before the court. If they win, environmental advocates said, automakers could be forced to produce a fleet of vehicles that emit less pollution.

“Everything now hinges on what the Supreme Court does,” said David Bookbinder, a lawyer for the Sierra Club, one of the environmental groups that pressed the issue.

Until now, the threat of global warming has prompted much public debate, but little governmental action.

The legal dispute turns on standards set during the 1970s when Congress adopted the Clear Air Act. One provision requires the government to regulate “any air pollutant” from motor vehicles or power plants that may well “endanger public health or welfare” – including by affecting the “weather” or “climate.”

In 1999, a group of environmental scientists pointed to this legal standard and petitioned the EPA to set new regulations to confront the problem of global warming.

They said the evidence showed that pollutants from cars, trucks and power plants were endangering the public welfare by changing the climate. They called upon the EPA to restrict emissions of carbon dioxide, methane, nitrous oxide and hydrofluorocarbons.

Four years later, the EPA under the Bush administration rejected the petition. It questioned the link between auto emissions and global warming and concluded that new regulations were not required. Last year, that conclusion was upheld in a 2-1 ruling by the U.S. Court of Appeals for the District of Columbia.

Usually, federal agencies are given broad leeway to interpret the laws they are supposed to administer. In this case, however, the 12 states joined with environmentalists and went to court to challenge the EPA’s decision.

In their appeal to the Supreme Court, they argued that the Clean Air Act required regulation of greenhouse gases and that EPA was defying this requirement.

The 12 states are California, Connecticut, Illinois, Massachusetts, New Jersey, Maine, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington. Three cities – New York, Baltimore and Washington, D.C. – also joined the appeal.

At least four of the nine justices must vote to grant an appeal, and on Monday, the court issued a one-line order saying it had agreed to hear the case of Massachusetts v. EPA.

The Supreme Court has been closely divided along ideological lines on issues of environmental regulations.

Last week, the justices were split on whether the government still had broad authority to regulate wetlands. Justice Anthony M. Kennedy wrote a pivotal opinion that fell in between the views of the four conservatives and four liberals, preserving most of the government’s authority to protect wetlands. His vote is likely to be crucial as well on the issue of greenhouse gases.

Environmentalists hailed the court’s decision to hear the case.

“The Bush administration has continually tried to say that it’s not their job to fight global warming. In fact, they have both the legal and moral responsibility to tackle global warming pollution,” Bookbinder said.

California Attorney General Bill Lockyer said he was confident the Supreme Court “will make history by striking down the Bush administration’s stance” against regulating greenhouse gases.

“Science overwhelmingly documents the certainty of global warming, and we must act now in order to save our planet from disastrous impact on our global environment, health and economy,” he said.

But a spokeswoman for the EPA said the agency had made the right decision by relying on voluntary moves by manufacturers.

“The Bush administration has an unparalleled financial, international and domestic commitment to reducing greenhouse gases,” said Jennifer Wood, an agency spokeswoman.