Washington ? Frustrated by Bush administration inaction on global warming, states and environmentalists urged the Supreme Court Wednesday to declare greenhouse gases to be air pollutants that the government must regulate.

The court’s first case on the politically charged topic showed an apparent split between its liberal and conservative justices, with Anthony Kennedy potentially the decisive vote in determining whether the administration must abandon its refusal to treat carbon dioxide and other greenhouse gases as air pollutants that imperil public health.

Justice Samuel Alito, who with Chief Justice John Roberts seemed most skeptical of the states’ position, said that even in the best of circumstances, the reduction in greenhouse gases would be relatively small.

Justice David Souter indicated that every little bit would help. “They don’t have to show that it will stop global warming. Their point is that will reduce the degree of global warming and likely reduce the degree of loss,” he said.

The case involves whether the Environmental Protection Agency must regulate emissions of greenhouse gases from new vehicles under a provision of the Clean Air Act. When a decision comes sometime before July, it could have a significant ripple effect that could extend to power plants as well as states’ efforts to impose more stringent regulations on car tailpipe emissions.

Many scientists believe that 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.

Carbon dioxide, the principal “greenhouse” gas, 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.

“We own property, 200 miles of coastline, that we’re losing,” Massachusetts assistant attorney general James Milkey said on behalf of 12 states and 13 environmental groups that sued EPA.

Deputy Solicitor General Gregory Garre, representing the Bush administration, cautioned justices that EPA regulation could have a significant economic impact on the United States because 85 percent of the U.S. economy is tied to sources of greenhouse gas emissions.

Garre also argued that the EPA was right not to act given “the substantial scientific uncertainty surrounding global climate change.”