U.S. congressional passage of a bill limiting Japanese car exports would open the door for a return to the international trade protectionism of the 1930s, a ranking Japanese official predicted today.

Naohiro Amaya, one of the government's leading authorities on international trade, said the restrictive legislation would be followed by similar moves in other countries.

The result, he said in an interview, would be "damage to the free-world economies. It would open the door to the retrogression of the 1930s."

Amaya, vice minister of international affairs for the Ministry of International Trade and Industry, is one of the key officials shaping Japan's trade policy. He is expected to visit Washington next week for a final sounding on the auto export controversy before his government makes a decision on whether to restrict sales in the United States.

His views on the dangers of American quota legislation reflect the standard policy at his ministry and explain why it has been anxious to curtail Japan's exports, a position strongly opposed by the auto industry and by some other important government officials.

Amaya said the ministry believes legislation introduced by Sen. John Danforth (R-Mo.) is likely to be enacted, forcing a reduction of Japan's exports to 1.6 million passenger cars a year for each of the next three years.

To avert what officials say would be the disastrous consequences of a formal quota, the ministry is urging that the government and auto makers here join to reduce exports by their own initiative.

Without voluntary export reductions, Amaya insisted today, European contries would enact similar restrictions and they would spread to major trade items other than automobiles. Canada also would limit Japanese car imports and the French have indicated they are prepared to protect other industries, such as electronics, that are considered endangered by Japan's export surges, he said.

The issue reaches a showdown here within a week. On Saturday, International Trade Minister Rokusuke Tanaka meets with seven auto company executives in attempts to win approval of a unilateral export reduction, and a final decision is expected to be made at the highest levels next week.

The auto makers are not expected to grant Tanaka the power he wants. They have agreed only to hold exports to last year's level of about 1.82 million cars for one year, far too little in the ministry's view to save Japan from Danforth's bill.

The ministry favors a cutback lasting somewhere between one and three years. Contrary to Japanese press accounts early this week, Amaya said the ministry has not picked 1.7 million cars as its export target for this year. He would not say what the ministry's target is or even if it has decided on one.

One reason for the feud between the ministry and the auto industry is a somewhat differing perception of the Danforth bill's chances One Toyota executive has expressed a personal opinion that it will not be enacted.

The ministry feels differently. "We think the dangers [of its passage] are too serious to take that risk," Amaya said. Both the government and industry follow congressional politics closely and in this case have come to differing conclusions.

Amaya also said the ministry has not come to any conclusion about how to enforce an export limit if one is agreed upon. Until recently, it appeared likely Japan's export control act would be invoked. That would be the most certain way of protecting the auto companies from antitrust suits in the United States.

But invoking that act in this case might cause demands for similar action by European countries, Amaya said, adding the government is still "groping" for a solution less formal than the export control act and something more strict than its usual formula of "administrative guidance."

Amaya contended that the implications of the Danforth bill would go far beyond the case of Japanese automobiles. It would be followed, he asserted, by protectionist legislation in other countries aimed at American exports as well as Japanese exports.

"I can understand the political pressures that he [Danforth] is facing on the American side," Amaya said. "I wish he would understand the political difficulties that the law would trigger off on the international side."