LOS ANGELES - A mandate that envisions exhaustless electric vehicles crowding California has made the air cleaner and spurred technological advances in everything from computers to hearing aids.
But a decade after its inception, the zero-emission vehicle rule - the first of its kind in the nation - has little to show in the way of actually creating zero-emission vehicles.
The Air Resources Board, the state's top air-quality enforcer, will consider Thursday and Friday whether to relax regulations that by 2003 call for an estimated tenfold increase in electric vehicles, from the roughly 2,300 that now silently rush along the state's smog-troubled streets and highways.
Air quality officials and environmentalists say the success of the mandate could point the way for similar experiments in polluted regions elsewhere. Mass producing electric vehicles for Californians will drive down their costs and eventually make them more available across the country.
More than 100 speakers - including a string of top auto industry officials who want the requirements cut back - have signed up to speak before the board, which has received 18,000 letters on the topic. That's as many as it has received on any one subject, said board spokesman Jerry Martin.
''Many of the letters are from people who say, 'I'd like to buy one but I can't find one,''' he said.
The board must renew the mandate every two years. This time, it is likely to ask for some revisions - including finding money to help subsidize electric vehicles. Board staff have conceded that the goal of 2003 is unlikely to be met without further assistance from state agencies.
Already, some help may come from the Legislature. A bill in the state Senate would offer $3,000 credits to people who buy zero-emission vehicles.
But that falls well short of covering the cost difference between electric and gasoline-powered cars, which runs from $7,500 to $20,000, according to air board staff estimates.
The Alliance of Automobile Manufacturers, a coalition including most major automakers, puts the cost of the vehicles at the high end - $20,000 more than a gas car - and estimates it will cost $1 billion a year to meet the mandate's requirements, said alliance spokeswoman Gloria Bergstrom.
The rules allow automakers to meet some of the mandate with near-zero-emission vehicles, but Bergstrom said most automakers don't have models that can meet the near-zero standard.
The alliance wants the mandate overturned, even though that's an unlikely prospect.
When the mandate was first approved in 1990, air board staff estimated the electric-car requirements would keep 14 tons of pollution out of the air each day, but that figure has fallen to a ton a day. Passenger cars in California emitted an estimated 1,530 tons of hydrocarbons and oxides of nitrogen a day in 1996.
Nevertheless, Martin, the air board spokesman, said whatever the effect on pollution, the rules will continue to prod automakers to make cleaner cars.
A study by two University of California, Davis, professors on contract for the air board found that the creation of the air rules led to a sharp increase in public and private electric-car research. That led to improvements in battery technology that has improved not only electric cars, but computers, cellular phones and hearing aids as well, the study found.
Martin added that many of the pollution-cutting advances automakers have made - even those not involving pure electric vehicles - stem from the rules.
''Without them, there certainly would be no such thing as a Prius or an Insight - or if they were they'd just be cars you saw at an auto show,'' he said.
The Toyota Prius and Honda Insight are ''hybrid'' vehicles that use a combination of gasoline and electric power. Compared to gasoline alone, the combination is cleaner-burning and more than doubles the range between fuel-ups - a key problem for electric vehicles than need frequent recharging.
The market for electric vehicles is hot by the measure of Terry O'Day, vice president of planning and operations for EV Rental Cars. The Los Angeles-based company rents alternative-fuel vehicles out of six airports in California, and will expand over the next two months into Phoenix and Las Vegas.
The company, which received a $300,000 grant from the air board and the Los Angeles area's air quality district, rents out 135 electric, natural gas and hybrid vehicles. Demand is high for the electrics, O'Day said, adding that the company will buy more when they become available.
''The niche is small, but it's there,'' he said.