Thursday's decision is expected to affect 12 other U.S. states that had adopted California's target for zero-emission vehicles, defined as those powered solely by batteries or hydrogen fuel cells.
The California Air Resources Board voted to lower by 70 percent the number of those vehicles that automakers must sell here and in the states that intended to follow California's get-tough rules for vehicle emissions.
Instead, the air board said the six largest automakers must sell nearly 60,000 plug-in hybrid vehicles in California while they develop the more advanced technology that will allow mass production of pure zero-emission vehicles.
Board chairwoman Mary Nichols described the move as a major step toward putting cleaner cars on the road. The plug-in hybrids envisioned by the air board have yet to be produced but are in development by several automakers.
"We're introducing a whole new category of vehicles to the public," Nichols said. "I don't think it's a step backwards in the real world."
In essence, the air board took two steps Thursday: It cut the number of zero-emission vehicles it wants on the road by 2014, while at the same time offering an alternative - the gas-electric hybrids.
Environmentalists and health advocates criticized the lowering of the zero-emission goal for vehicles. They said the threats posed by global warming, combined with rising gasoline prices, lend urgency to greatly reducing vehicle emissions.
"We are disappointed. We think this proposal doesn't take us on the road to meeting the state's long-term global warming goals," said Spencer Quong, a senior vehicles analyst at the Union of Concerned Scientists.
Auto manufacturers said they could not meet the California standard and needed more time to make affordable hydrogen and battery-powered cars.
"Pushing this technology into the market before they are commercially viable ties up resources that could be better utilized by advancing core technologies," said Sara Rudy, an emissions regulatory manager at Ford. "It is important at this stage to be nimble."
The other manufacturers that must comply with the rules are General Motors Corp., Toyota Motor Corp., Honda Motor Co., Chrysler LLC and Nissan Motor Co.
General Motors is developing a rechargeable vehicle it hopes to have on the market in 2010. The Chevy Volt would run on a battery for 40 miles, and then fuel would power the on-board generator, GM spokesman Dave Barthmuss said.
California adopted its zero-emission vehicle mandate in 1990 as part of an attempt to reduce smog-forming emissions such as nitrogen oxide.
The rule required that 10 percent of new cars sold in the state by the country's six leading auto manufacturers be completely nonpolluting by 2003.
The rules have been modified four times since they were introduced. The biggest change came in 2003, when the Air Resources Board significantly scaled back the mandate and ruled that hydrogen cars, hybrids and cleaner-burning gasoline vehicles could meet the state's goals.
The regulators were concerned that battery-powered cars could not be mass-produced and favored hydrogen cars. They also faced a lawsuit from the auto industry.
Although some lower-emission vehicles - especially hybrids - have begun making an impression in the marketplace, the main automakers still do not have a commercial zero-emission vehicle.
The revised 2003 rules set a goal of putting at least 25,000 zero-emission cars on the road in California by 2014, far below the original 10 percent mandate.
The rules adopted Thursday put the number of zero-emission vehicles required nationwide by 2014 at 7,500, a 70 percent reduction from the 2003 target.
The 12 other states that adopted the California standard are Connecticut, Maine, Maryland, Massachusetts, New Mexico, New York, New Jersey, Oregon, Pennsylvania, Rhode Island, Vermont and Washington.
Arizona, Colorado, Florida and Utah are considering it, according to the Air Resources Board.