General Motors Corp. yesterday gave auto-safety advocates one of their biggest victories in years by announcing that it will offer air bags as options on its 1988-model cars.

GM did not say how much it will charge for air bags or how many cars it expects to equip with them. Industry sources speculated that the company could supply in excess of 200,000 air bags a year.

GM, the nation's biggest auto maker, has long been regarded by auto safety advocates as the leading opponent of passive-restraint passenger safety devices such as air bags and automatically closing seat belts.

Air bags are flexible containers mounted in the steering column or on the dashboard that are designed to inflate automatically in a collision. Triggered by the rapid deceleration of a crash, the bags rapidly inflate to protect motorists, then instantly deflate.

GM said it will offer air bags only on the driver's side as a test of consumer demand.

The giant auto maker's decision to follow West Germany's Daimler-Benz AG and Ford Motor Co., America's second-largest auto maker, in offering air bags as options signals a major breakthrough in a battle that started in 1970, consumer advocates said.

Mercedes-Benz and Ford cars have had air bags available as an option on a limited basis for about $800 since last year. This year, Mercedes has made the device standard equipment, and Ford has offered the bags on a wider variety of its mid-size cars.

Conventional wisdom among auto-safety advocates and industry analysts has been that as long as GM stayed out of the market, air-bag acceptance would grow slowly.

"If GM genuinely gets into a competitive battle with the other manufacturers who are offering air bags, if GM markets air bags the same way it markets air conditioning, stereos and automatic transmissions, the competitors had better watch out," said Clarence Ditlow, an often-vehement GM critic who is director of the Washington-based Center for Auto Safety. GM potentially could turn air bags into standard equipment in all cars sold in the United States, Ditlow said.

GM had offered air bags on its 1974 through 1976 models. Although the company then said it was prepared to sell 100,000 air bags a year, it sold only 10,000 during the entire three-year period.

Yesterday, consumer advocates generally praised GM's decision to try air bags again.

"It's about time," said Joan Claybrook, a former administrator of the National Highway Traffic Safety Administration, who serves as director of Public Citizen, a Washington-based consumer lobby. "This is the breakthrough that we've all been waiting for. GM was the biggest holdout," Claybrook said.

The GM air-bag announcement was made yesterday in Chicago by the company's chairman, Roger B. Smith, who said the decision stems from "a new interest in safety" on the part of car buyers nationwide.

Passage of state mandatory seat-belt laws also "is contributing to public acceptance of restraints of all kinds, including air bags," Smith said. "We're offering this system in response to what we think our customers want -- rather than in response to a government mandate -- and that's the way it ought to be."