Executives of Japanese automobile companies fear an outbreak of "Japan bashing" in the United States over the next two years as their cars continue making deep inroads in the American market.

By next fall, the industry expects Japanese car production at U.S. plants to exceed 1.6 million units a year, with the total topping 2 million units by 1992. Combined with the 2.3 million autos that Japan is permitted to ship to the United States annually, this brings to 4.3 million the number of Japanese cars likely to hit the U.S. market that year.Industry analysts surveyed here agreed on the possibility that by the fall of 1992 one of every two cars sold in the United States will be Japanese since there are signs of a decline in U.S. auto sales from the recent level of 10 million units a year.

One senior Japanese auto executive, who requested that his remarks not be directly attributed, projected that overall car sales in the United States will decline to 9.5 million units this year. "So it looks like we stand a good chance of taking half the U.S. market in 1992 under current projections," he said.

He admitted, however, that with Japanese auto production in the United States shifting into high gear in the intervening months, "a sudden supply overload could trigger another round of Japan bashing amid demands by American carmakers for a further reduction in the self-imposed export quota."

At some point, he said, Japanese automakers may have to settle for slightly more than a third of the U.S. car market.

Actually, in contrast with steadily expanding Japanese production at U.S. plants, Japan's car exports to the U.S. market probably will dip to no more than 1.6 million units in 1992. Last year, despite the higher quota, the Japanese shipped just under 2 million units to the United States.

To head off bashing by frustrated U.S. automakers, Japanese carmakers with plants in the United States intend to step up exports of U.S.-assembled vehicles to Japan, Taiwan and other markets, these analysts say.

Honda Motor Co. and Mazda Motor Co. were the first to export U.S.-assembled cars to Japan, and Mitsubishi Motors Corp., Toyota Motor Corp. and Nissan Motor Co. intend to follow suit soon.

Toyota, which is already planning to export 18,000 U.S.-assembled autos to Taiwan by the end of this year, has announced plans to ship 40,000 units annually from its Kentucky plant to Japan starting in 1992. In addition, Mitsubishi is about to begin exporting to Europe sedans produced jointly with Chrysler Corp. in the United States.

Exports of these U.S.-assembled autos are expected to total 40,000 units this year and to climb to 150,000 units or more by 1992.

Fuji Heavy Industries Ltd. recently began shipping to its Taiwan subsidiary its own cars assembled in the United States by Subaru Isuzu Automotive Inc. But analysts say it is too early to project what the yearly volumes will be.