NOT SO LONG ago the negotiations every three or five years between the United Auto Workers and the Big Three auto makers were choreographed as precisely as the changing of the guard at Buckingham Palace. The union trumpeted its demands for giant wage and benefit increases, the companies called grimly for economic realism, and -- sometimes after a strike, sometimes not -- both sides would impose a news blackout and settle on a liberal package the size of which they both could have predicted in advance. The cost, they assumed, would be passed along to consumers, who were thought to have an inborn desire to buy a new American car every couple of years.

Now the scenario -- not to mention the audience -- is different. The UAW isn't seeking vastly higher wages and benefits this year; it is concentrating on "job security," maintaining the number of jobs, vastly reduced over the past few years. The companies, on the other hand, want to maintain the right to buy and/or produce cheap parts abroad. The UAW commissioned a national poll whose results suggest Americans wouldn't mind paying somewhat more for cars to keep jobs in the U.S.A.; and it is running $2 million worth of TV ads to make that case. The companies, for their part, say higher wages would raise prices and reduce competitiveness, and that workers should concentrate on improving product quality.

Both auto workers and auto makers have discovered, painfully, that Americans can get along without buying new American cars a lot longer than the late Alfred P. Sloan would have dreamed. And both understand that they must make their case to public opinion generally -- because their fate depends to an uncomfortable extent on the political process. Detroit is currently shielded from the full force of Japanese competition by "voluntary" import agreements, and is nervous lest the Reagan administration, in theory committed to free trade, refuse to renew them at current levels.

Auto executives survived a scare this year when trade negotiator Bill Brock criticized their high salaries and bonuses and suggested import quotas might no longer be needed; but no one in the administration seconded his motion. The UAW, which made major concessions in 1982 to help the industry recover, now understands that demands for big increases in pay and benefits would jeopardize the quotas as well; hence the effort to portray its demands as an attempt to protect current jobs.

In theory everyone involved would like the auto business to be conducted without government interference. But it's already too entangled with and dependent on government for that, and despite its retrenchment it remains so big no government can ignore its problems. Mr. Reagan, who called on workers and companies to show "restraint," may have done so only as a candidate whose cause would be hurt by a strike. So, while the campaigning Republicans talk about freedom from regulation and the Democrats talk about fairness to the little guy, the serious business of keeping the now profitable auto companies in business and the well-paid remainder of the auto work force on the job continues.