This push is especially strong in California, whose tough regulations have encouraged the big automakers to test a range of alternatives to traditional gas engines, from hydrogen fuel-cell vehicles to cars that run on natural gas.

But the most active grass-roots environmental campaign favors plug-in hybrids, which store power in rechargeable batteries and can run only on battery-power for short trips in congested cities like Los Angeles.

"It has the potential to reduce oil consumption by millions of barrels per day," said Long, who has lobbied General Motors Corp. and Ford Motor Co. to get behind the technology. "If the question is what can we do in the short-term, there is only one answer, and that's plug-in hybrids."

The auto industry, which has a history of resisting environmental regulations, is now looking to court both activists and the growing number of US drivers who say they are willing to pay more for an alternative to a traditional gas-powered vehicle.

The Los Angeles Auto Show, which opens to the public on Friday, is becoming a major showcase for major automakers to display upcoming green vehicles in a market where they are likely to find the fastest and greatest acceptance.

This year, GM is using the LA Auto Show to draw attention to a pair of current-generation hybrids: the Saturn Aura and the Yukon sport-utility vehicle.

GM, BMW AG, Honda Motor Co. and Nissan Motor Co. will also show off hydrogen-powered vehicles.

But environmental activists like Long will be watching most closely for what the companies signal about their interest in plug-ins.

No automaker has yet committed to build a plug-in car, not even Toyota Motor Corp., whose Prius leads the market for current-generation hybrids.

PIMP MY PRIUS

Looking to jump start broader commercial interest, one San Francisco-area nonprofit group, CalCars (http://www.calcars.org/), has helped build about 20 plug-ins since 2004 by hacking and tricking out the Prius.

The cars are outfitted with new lithium-ion battery packs, which hold a charge longer than more common nickel metal hydride batteries.

In a parallel effort, a small California company, EnergyCS (http://www.energycs.com/), is planning to convert new Prius models beginning next year at a cost of an additional $12,000 to consumers.

CalCars founder Felix Kramer said the goal would be to persuade big carmakers to switch to plug-in technology quickly.

"I'm kind of looking at this like Pearl Harbor, where the auto industry went from making cars and trucks to planes and tanks in just a year."

He said part of the appeal of the plug-in technology is its potential to reduce the US reliance on oil shocks, since the cars would draw power partly from the electric grid.

But critics argue that, depending on how cleanly the electricity is generated, plug-in technology would just shift the source of pollution from the car to the power generator, which in some cases is fueled by coal.

Sherry Boschert, a member of the advocacy group Plug In America and author of a new book on plug-ins called "The Cars that Will Recharge America," said she worried development efforts could also be slowed by arguments about the technical limits of current batteries.

Some automakers have signaled that they would prefer to wait for the emerging class of lithium-ion car batteries to develop before pressing ahead with plug-ins, she said.

"These cars are doable today," she said. "At what point do you have to say that good is good enough."