In the debate on air bags and other automatic crash protection in cars, two facts are unassailable. First, no technology for crash protection has been more tested, proven more reliable or promised to save more lives than the air bag. Second, nothing in the 1966 highway safety law says that the Department of Transportation can back away from a rule because GM, Ford or Chrysler aren't selling as many cars as they'd like to.

Despite this, the Reagan administration, through Transportation Secretary Drew Lewis, is proposing to change the current rule that requires air bags in large cars in 1982, medium-sized cars in 1983 and small cars in 1984. In the history of passive restraints, which goes back to a 1969 Nixon administration decision requiring air bags, some five delays have been won by the industry. Every delay had been used for one purpose: to lobby for another delay.

In the latest proposal, Lewis echoed the often-heard industry arguments, ones that safety offcials have been rejecting for 12 years: Detroit has enough woe without more regulations, and air bags in big cars mean that smaller foreign cars would gain a competitive edge. In other words, as Ralph Nader points out, "The sales curve for the industry is deciding the death curve on the highway."

With the Reagan budget trimmers promising not to hurt "the truly needy," it is no doubt comfort for some that there is concern about the needy auto industry. But a common theme runs through past efforts to "help" Detroit. After political pressures build to push auto makers into producing fuel-efficent, low-polluting and sturdier, less fragile cars, the pressures ease off. It is now understood, though, that these relaxations in getting the industry to make safe, clean and mechanically sound cars have been no favor at all .

It has been a reinforcement of backwardness, coming when many foreign competitors have been energetically moving forward. Mercedes has an air bag in many of its cars sold in Germany and reportedly is soon to offer them in the United States. Another European firm is equipping cars with an extra-safe windshield which does much to eliminate decapitations and facial lacerations in frontal crashes.

Instead of pushing past this competition and gaining the edge through the sale of safe cars -- and advertising this safety with the passion that horsepower, sleekness and bucket-seat commfort have been advertised -- auto leaders like Henry Ford II, Thomas Murphy and Lee Iacoca have consistently retreated.

The seeking of another air-bag delay might be a temporary expedient. But it won't help the industry to gain long-haul stability. What's needed in Detroit is commitment to act like entrepreneurs using competitive, socially responsive technology in the marketplace.

The pervading fear of the industry is that safety costs too much and the public, at some point, will balk.

But according to the Center for Auto Safety, air bags will have a 4-to-1 cost-effective ratio. For every dollar spent for them, four dollars are saved in accident costs. If the Reagan administration is so ardently anti-inflation, why isn't it seizing the chance to lower the massive expenses of highway crashes? Researchers at the Harvard School of Public Health report in the current Socioeconomic Newsletter that in 1975, after cancer, the deaths and injuries in motor vehicle accidents created the nation's heaviest economic costs: $14.5 billion.

Safety officials estimate that if the original air-bag rule had been enforced, as former secretary of transportation John Volpe ordered in 1969, as many as 9,000 lives a year would have been saved. During all these years of death and injury, countless citizens have been denied their right to safety. The choice is either avoid using cars totally or be subjected to the risks imposed by the industry on motorists and passengers every time they go out on the road.

As for getting American car makers to market safety, the citizens can't persuade them and now the Reagan administration won't force them. With highway death on the rise again, the losses continue to be staggering.