WASHINGTON - The Supreme Court ordered the federal government today to take a fresh look at regulating carbon dioxide emissions from cars, a rebuke to Bush administration policy on global warming.

In a 5-4 decision, the court said the Clean Air Act gives the Environmental Protection Agency the authority to regulate the emissions of carbon dioxide and other greenhouse gases from cars.

Greenhouse gases are air pollutants under the landmark environmental law, Justice John Paul Stevens said in his majority opinion.

The court's four conservative justices - Chief Justice John Roberts and Justices Samuel Alito, Antonin Scalia and Clarence Thomas - dissented.

Many scientists believe greenhouse gases, flowing into the atmosphere at an unprecedented rate, are leading to a warming of the Earth, rising sea levels and other marked ecological changes.

The politics of global warming have changed dramatically since the court agreed last year to hear its first global warming case.

Democrats took control of Congress last November. The world's leading climate scientists reported in February that global warming is “very likely” caused by man and is so severe that it will “continue for centuries.” Former Vice President Al Gore's movie, An Inconvenient Truth - making the case for prompt action on climate change - won an Oscar. Business leaders are saying they are increasingly open to congressional action to reduce greenhouse gas emissions, of which carbon dioxide is the largest.

Carbon dioxide is produced when fossil fuels such as oil and natural gas are burned. One way to reduce those emissions is to have more fuel-efficient cars.

The court had three questions before it.

€ Do states have the right to sue the EPA to challenge its decision?

€ Does the Clean Air Act give EPA the authority to regulate tailpipe emissions of greenhouse gases?

€ Does EPA have the discretion not to regulate those emissions?

The court said yes to the first two questions. On the third, it ordered EPA to re-evaluate its contention that it has the discretion not to regulate tailpipe emissions. The court said the agency has so far provided a “laundry list” of reasons, including foreign policy considerations.

The majority said the agency must tie its rationale more closely to the Clean Air Act.

“EPA has offered no reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change,” Stevens said. He was joined by his liberal colleagues, Justices Stephen Breyer, Ruth Bader Ginsburg and David Souter, and the court's swing voter, Justice Anthony Kennedy.

The lawsuit was filed by 12 states and 13 environmental groups that had grown frustrated by the Bush administration's inaction on global warming.

In his dissent, Roberts focused on the issue of standing, whether a party has the right to file a lawsuit.

The court should simply recognize that redress of the kind of grievances spelled out by the state of Massachusetts is the function of Congress and the chief executive, not the federal courts, Roberts said.

His position “involves no judgment on whether global warming exists, what causes it, or the extent of the problem,” he said.

The decision also is expected to boost California's prospects for gaining EPA approval of its own program to limit tailpipe emissions of greenhouse gases. Federal law considers the state a laboratory on environmental issues and gives California the right to seek approval of standards that are stricter than national norms.