LOS ANGELES -- California air regulators have unanimously approved the world's most stringent rules to reduce auto emissions that contribute to global warming, a move that could affect buyers of cars and trucks from coast to coast.

Under the regulations adopted yesterday, the auto industry must cut exhaust from cars and light trucks by 25 per cent, and from larger trucks and sport utility vehicles by 18 per cent. The industry will have until 2009 to begin introducing cleaner technology and will have until 2016 to meet the new exhaust standards.

The move, by the California Air Resources Board, came despite vigorous opposition from officials in the auto industry, who argued that the board did not have the authority to adopt such sweeping regulations and that they could not be met by current technology.

The industry has threatened to challenge the regulations in court. Governor Arnold Schwarzenegger has expressed support for the proposals and pledged to fight any such lawsuits.

Heat-trapping greenhouse gases such as carbon dioxide and carbon monoxide are believed by many scientists to contribute to global warming.

Auto makers will be required to reduce emissions by way of such innovations as better air conditioners, more efficient transmissions and smaller engines.

Gloria Bergquist, speaking for the industry trade group Alliance of Automobile Manufacturers, said no decision has been made whether to challenge the regulations in court.

Ms. Bergquist said introducing the technology would be "almost as complicated as developing the first automobile." She also said that the regulations would reduce worldwide emissions of greenhouse gases by only "one-tenth of 1 per cent."

The new standards could have a coast-to-coast effect; California represents 10 per cent of the national auto market, and the auto industry often overhauls its cars to meet California's standards.

California is the only state able to set its own vehicle pollution standards. Other states can adopt either federal vehicle pollution standards, or California's.

Board members said they were disappointed auto makers did not accept invitations to work with them on the regulations.

"The response, the silence, was deafening," chairman Alan Lloyd said. "I hope that we still can work together on this tremendously important issue. The stakes could not be higher."