California’s once-ambitious, always-controversial plan to require automakers to sell electric cars faces a vote this week that, advocates say, would effectively gut the program.

Thursday, the state Air Resources Board meets in Sacramento to consider a plan to cut the number of pure electric vehicles that carmakers would be required to sell over the next few years from 25,000 to 2,500.

When the state enacted this zero-emission vehicle mandate in 1990, it called for 10 percent of new-vehicle sales from big automakers to be all-electric by 2003, or about 100,000 cars or more a year. That requirement was eventually delayed by several years and reduced to the current level.

At the board’s request, the ARB staff revisited the mandate and produced a 52-page proposal that concluded battery-electric and hydrogen fuel-cell vehicles remain too costly and still face too many hurdles for mass sales in the state. Instead, requiring automakers to sell a mix of cleaner-burning gasoline cars, hybrids and plug-in hybrids would be more realistic.

The changes “keep our commitment to zero emissions alive while appropriately reflecting the pace of the technology,” said Analisa Bevins, chief of the air board’s sustainable transportation technology branch.

But advocates aren’t so sure. “The low numbers do turn the clock back on progress and certainly send the wrong signals to the public and the technology producers,” said Bonnie Holmes-Gen, policy director for the American Lung Association of California.

If the board approves the changes, said Ze’ev Drori – chief executive of Tesla Motors, the San Carlos company that put its $100,000 electric roadster into production this month – it would “make a mockery of CARB itself.”

Even Mary Nichols, chair of the 11-member board, isn’t sure.

“We’re all looking for ways that we can strengthen the staff report to make it a little bit more aggressive in terms of numbers of vehicles,” she said.

Asked directly if she would vote to approve the amendments, she said, “I’m going to be supporting some changes.”

The original mandates were written when there was much less awareness of greenhouse-gas emissions and California hadn’t enacted its groundbreaking global-warming legislation, AB 32, which requires dramatic cuts in the state’s total production of greenhouse gases.

Nichols wants a “rethinking of the whole ZEV mandate program in light of our AB 32 needs.”

That echoed a comment by Holmes-Gen, whose group funded a study that suggested that weakening the ZEV mandate would be bad for the health of Californians.

“It’s disappointing that the proposal is not linked to the aggressive statewide targets for greenhouse gas reduction by 2050,” she said.

Tesla’s Drori said the changes to the ZEV mandates would “needlessly weaken” the program.

He takes particular umbrage at the fact that reducing the number of required electric cars would cut the number of credits his company could earn – and sell – for making them. Those funds would help defray Tesla’s development costs, he said.

California once seemed poised to change what people drive when the Air Resources Board issued the ZEV mandates in 1990.

But automakers launched a legal battle against them, delaying their implementation.

Ultimately, a few thousand electric vehicles from General Motors, Honda, Toyota and others were sold or leased in the state. And, as the ’90s ended, first Honda, then Toyota, and later other automakers introduced hybrids, higher-mileage cars carrying both gasoline engines and electric motors.

In 2003, ARB shifted direction, saying the electric-car technology wasn’t progressing and instead agreeing to let automakers make cleaner gasoline cars and hybrids while they worked toward pure electrics.

That decision, along with GM’s move to stop leasing its EV1 and to crush many of the vehicles that it took back, led to “Who Killed the Electric Car?,” a documentary by Chris Paine.

One star of that movie, Chelsea Sexton, is now executive director of Plug-In America, which advocates for production of plug-in hybrid and electric vehicles.

The air board staff listens too much to automakers, she said, who tell it that batteries are and will remain too expensive. “Certainly there’s a history here of automakers low-balling CARB. No industry wants to be regulated, so they want to make this look as difficult as possible,” Sexton said.

If the changes are approved, Sexton said, CARB will render itself irrelevant in future discussions about alternate-fuel technologies. “This is a fairly toothless piece of policy,” she said.