California won a major legal battle Wednesday in its fight to implement a global-warming law that would lead to steep increases in motor vehicle fuel economy.

A federal judge in Fresno tossed out a lawsuit filed by the world's major automakers that tried to overturn AB 1493, a law that requires a 30 percent reduction in greenhouse gas emissions by 2016.

The automakers had said the law was unconstitutional because it mandated a big jump in mileage standards - a matter that is under the authority of the U.S. Department of Transportation's National Highway Traffic Safety Administration. They further argued that the California standards would raise vehicle prices by as much as $6,000 per vhicle, leading to fewer sales and tens of thousands of auto-plant layoffs.

But U.S. District Judge Anthony Ishii rejected those claims, ruling that the goal of reducing greenhouse gas emissions and arresting climate change must go forward.

The judge's decision doesn't mean the law automatically takes effect. California still needs a waiver from the U.S. Environmental Protection Agency to implement AB 1493.

Last month the state sued the EPA to force a decision on its waiver request. On Wednesday EPA spokeswoman Jennifer Wood said the federal agency will rule on the request by the end of December. If the EPA turns down California's request, Gov. Arnold Schwarzenegger and other state officials have vowed to sue the government again.

The Fresno decision came as climatologists and policymakers, including many from California, convened in Bali, Indonesia, to hammer out a worldwide treaty on curbing greenhouse gas emissions.

State officials and environmentalists have said AB 1493 can be implemented using largely off-the-shelf technology. They say the additional cost per vehicle is probably no more than $1,800.

The Alliance of Automobile Manufacturers, responding to the decision, continued to criticize the California law, saying, "We need a consistent national policy for fuel economy, and this nationwide policy cannot be written by a single state or group of states - only by the fedeal government."

The alliance noted that leaders of Congress, working on a new federal energy bill, recently agreed to raise fuel economy standards for all vehicles from an average 25.3 mpg to 35 mpg by 2020. The bill has passed the House but not the Senate, and may run aground because of issues not related to fuel economy.

The judge's decision was greatly influenced by two earlier court cases. Last spring the U.S. Supreme Court ruled that the federal EPA had the duty to regulate greenhouse gases. More recently, a federal judge in Vermont threw out the automakers' lawsuit over a copycat law.

Vermont is one of 11 states that have adopted California's standards; five others are considering doing so. But all are on hold pending the EPA's decision on California's waiver request.

Environmentalists hailed Judge Ishii's ruling. "We keep winning," said David Bookbinder, a lawyer with the Sierra Club, which participated in the case. "The courts are simply not buying (the automakers') arguments."

He said he wouldn't be surprised if the automakers file an appeal, adding: "Sooner or later they're going to have to stop throwing lawyers at the problem and start hiring engineers."