THERE HAS BEEN no better show in town than the parade of witnesses before the International Trade Commission, which must decide -- within a few days after the presidential election -- a multibillion-dollar question: Has the U.S. auto industry been damaged by unfair competition from Japanese imports?

An unusual alliance of American trade unions and the Ford Motor Co. has demanded that the ITC recommend to President Carter the imposition of a quota system to chop off Japanese sales. Ford's chief executive Philip Caldwell, suggested that for the next five years the present importation rate of nearly 3 million Japanese cars and light trucks be slashed to 2 million.

The Ford - UAW call for radical surgery was contested strongly not only by Japanese exporters but by U.S. importers and representatives of U.S. consumer groups. In their briefs, they argue that Detroit can blame no one, outside of its own boardrooms, for bum decisions made as late as 1978 that kept the big companies producing big cars.

But how about Caldwell's frightening suggestion that quota relief is needed not only to improve the companies' profit-loss positions but to preserve the U.S. auto industry in the interest of American security? Caldwell, an articulate spokesman for a company in trouble, made the argument in a luncheon conversation with a few columnists that the industry's very survival is at stake.

Kenichi Furasawa, an adviser to former premier Takeo Fukuda and now a critic and commentator in Japan, told me last week that he thinks Caldwell can hardly be serious, given the fact that about $80 billion is already blueprinted for expansion of the U.S. auto industry over the next five to six years.

MOREOVER, if Caldwell had real concerns about the survival of the U.S. industry, it is unlikely that he would be deep in negotiations with Toyota on joint production ventures.

Furasawa suggests, nonetheless, that "there must be fairness in trade. No industry has the right to export unemployment to another nation in order to maximize its own profits." He thinks that the Japanese government should be persuading the powerful Japanese auto firms to work out an "orderly marketing agreement" to slow their exports to the United States, taking into account the need to protect the interests of American consumers.

Caldwell himself would have preferred the voluntary route to mandatory quotas, which run the risk of retaliation. Had the Japanese been reasonable earlier, he maintains, the industry would not have been forced "to go into the gutter" by pursuing a quote case.

Nonetheless, the ITC commissioners peppered Caldwell and other Ford executives with some perceptive questions. Why, for example, did it take Ford so long to anticipate the demand for small cars? Why did it then take Ford so long to produce its small cars? And why doesn't General Motors claim to be in the same fix as Ford, seeking the same remedy?

The weakness of the case for cutting the Japanese back by 1 million cars and light trucks can best be seen in an examination of testimony by a number of industrial unions supporting the UAW petition. In general, they say that if imports aren't limited, their members will suffer a permanent job loss and the communities in which they live will stay depressed.

But I could not find a single bit of proof in the briefs they submitted that imports were the cause of the problem -- merely that the union leaders "believe" the two things be linked.

IT IS NOT enough for them "to believe" or "to feel" imports are to blame. As William Tanaka, representing the Japanese automakers, said: "If Detroit had been producing in 1979 more of the type of fuel-efficient cars that it is producing today, many of the currently unemployed UAW workers would still be at work and these hearings would not have been held."

Nissan representative Alan Wolff, a former American trade negotiator under Robert Strauss, made the additional point that if the U.S. companies hadn't been pressed by Japanese competition, their fast-selling X cars and K cars would probably have been delayed even further.

Over the long term, the most hopeful sign for the U.S. industry is that the unions and workers are beginning to understand that the real test of survival lies in their own hands.Caldwell told us of a Ford secretary who had been made quality-conscious enough to write him that a staple in the seatbelt of the highly touted new Ford Escort did not give the image of a quality product.

"She was right," said Caldwell, who checked into it and ordered a change. Down the road, the question of whether American cars will be able to meet Japanese competition in quality and price terms depends on how seriously the on-the-line workers take the question of helping to boost productivity. "I can't tell you yet how that will come out," Caldwell said.