OTTAWA, April 5 - The Canadian government and nearly all the world's major automakers reached an agreement Tuesday under which the companies would voluntarily reduce the greenhouse gas emissions of their vehicles.

Under the agreement, the vehicle makers committed themselves to cutting a variety of emissions by 5.3 million metric tons by the end of 2010. The plan sets targets staggered over five years and requires regular reviews by a group of government and industry representatives.

How much cleaner the air may become as a result of the pact was unclear. John Bennett, a senior policy adviser for the Sierra Club of Canada, estimated that the new standards would be equivalent to an overall fuel efficiency improvement of 25 percent from current levels.

R. John Efford, the Canadian minister of natural resources, said Canada was able to come to terms with the industry through negotiation rather than legislation. He suggested that approach could be a model for Gov. Arnold Schwarzenegger of California.

"I should say to Arnold that I've envied him for some time," Mr. Efford said in a phone interview, referring to Governor Schwarzenegger's yacht and film career. "Now he should envy me. Our accomplishment in reducing greenhouse gas emissions starts with the signing."

Environmentalists here and in the United States said the Canadian pact may undercut an auto industry lawsuit against California's greenhouse gas emission reduction program.

"The same automakers who are suing California over its clean car standards are agreeing to essentially the same level of reductions in Canada," said Jason Mark, the clean vehicles director for the Union of Concerned Scientists in Berkeley, Calif.

Jerry Martin, a spokesman for the California Air Resources Board, part of the state's Environmental Protection Agency, welcomed the Canadian agreement.

"In California, we are just asking the car industry to do what they can do elsewhere in the world," he said from Sacramento.

The auto markets in Canada and California are roughly the same size. Mr. Bennett of the Sierra Club of Canada said that the two programs have roughly the same overall targets, though Canada's will be achieved more quickly.

"The automakers are going to have a heck of a time saying that what California wants is impossible," Mr. Bennett said.

The Alliance of Automotive Manufacturers, an American trade group that includes many of the 19 companies that signed the agreement in Canada, is leading the lawsuit against California.

The carmakers assert that California's emission rules effectively impose fuel-economy regulations, an area under federal control. Thus, the Canadian pact has no bearing on the case in California, said Eron Shosteck, a spokesman for the group in Washington.

The Canadian agreement does not specify how the automakers must meet their targets, nor does it require emissions reduction on a vehicle-by-vehicle basis. As a result, Mr. Bennett said, a carmaker may continue to sell gas guzzlers, offsetting their emissions by selling more low-emission hybrids.

Mark A. Nantais, the president of the Canadian Vehicle Manufacturers' Association, said most companies would make gradual changes rather than introduce drastic new technologies.

While many environmental groups in Canada and the United States praised the agreement, not all were impressed.

Matthew Bramley, the director of climate change at the Pembina Institute of Appropriate Development, said the agreement appeared to contain loopholes that would permit automakers to increase sales of inefficient light trucks without penalty. He was also concerned that the program was voluntary.

Mr. Efford added, however, that Canada was not abandoning its right to introduce regulations if the voluntary approach fails.

http://www.nytimes.com/2005/04/06/automobiles/06auto.html