SACRAMENTO, Calif. — California could become the first state to try easing global warming by limiting carbon dioxide emissions from cars if a bill approved this week by the state assembly becomes law.

The bill would give the Air Resources Board until January 2004 to adopt regulations that achieve the "maximum feasible and cost-effective reduction" of carbon dioxide from cars and light trucks.

Critics called it an exercise in environmental extremism and warned that the law might inconvenience some state motorists by forcing cars off the road.

"This bill gives the Air Resources Board — a group of unelected bureaucrats — the ability to create sweeping regulations in less than two years," said Minority Leader Dave Cox.

But supporters said the Legislature would have a year to review, and possibly revise, the regulations before they took effect — or scrap them altogether.

Carbon dioxide is an odorless gas that is not considered a direct threat to human health. But scientists say it is the biggest culprit in an increase in global temperatures.

Russell Long, executive director of the Bluewater Network, a San Francisco-based environmental group that proposed the bill, said some states are regulating carbon dioxide emissions from power plants. But no other state has tried to control carbon dioxide from autos, he said.

"This is a chance for us to be a leader again, on an issue that will continue to confront us and our children and their children in the future," said Assemblyman Dario Frommer.

California creates nearly 7 percent of global carbon dioxide emissions, and motor vehicles generate 57 percent of the carbon dioxide the state produces.