Nissan Motor Co. Ltd. may introduce larger-model autos into the United States because the U.S. auto market soon may be saturated with compact cars, Nissan's new president said in Tokyo yesterday.

The executive, Yutaka Kume, said Nissan has more than one new model under consideration, but he gave no details.

It was the first time any Japanese auto executive had mentioned publicly the possibility of selling a car larger than a compact model in the United States.

Kume also said at a news conference for foreign reporters that Toyota Motor Corp., Nissan's major rival and Japan's largest auto company, also might be thinking of offering a larger car for the American market.

He described as "only natural" reports that Toyota plans to invest in its own factory in the United States, in addition to its joint venture with General Motors Corp.

Toyota officials were not available for comment, but Japanese newspapers reported that Toyota is considering building a plant in the Midwest or the South to produce between 200,000 and 250,000 cars a year beginning in 1988. This would be in addition to the 250,000 cars Toyota and GM will be manufacturing at their joint-venture plant in Fremont, Calif., when that plant reaches capacity.

The cars produced at Fremont are being sold through GM's dealer network.

Meanwhile, in Detroit, sources said that Toyota is close to a decision on building an auto assembly plant in the United States and has discussed sites near Nashville, Tenn., and Kansas City, Mo.

Toyota probably will announce its decision this month and, if the plan is carried out, the plant will open in late 1987 or 1988, the sources said.

Takashi Ishihara, Nissan's chairman, backed up Kume's remarks about fears of a glut of Japanese small cars in the United States. He said he does not expect Japanese companies to be able to sell smoothly the 450,000 additional cars the Japanese government added this year to its self-imposed limit on exports to the United States.

Kume said Nissan's most important task would be to strengthen its domestic sales, with better products and a stronger sales network, to close the gap between it and Toyota. "We have been put on the defensive," he acknowledged.

Toyota has reigned for a generation as the top Japanese car marketer in the United States. However, the Japanese government's recent decision to continue auto import quotas for a fifth year infuriated Toyota officials. Also, Nissan and Honda Motor Co. Ltd. now are making cars in the United States and could threaten Toyota's grip on the No. 1 position.

"We're frustrated and our dealers are frustrated," said one Toyota official, who spoke on condition of anonymity. "We're No. 1 and we intend to stay there."

No specifics were given about the Nashville and Kansas City sites and the sources said other areas of the country may be under consideration.

Also in Tokyo yesterday, a spokesman for Mazda Motor Corp., Japan's third-largest auto maker, said that Mazda is considering a possible joint venture deal with Ford Motor Co. and Kia Industrial Co. of South Korea to make subcompact cars in Seoul.

The spokesman, commenting on a report in a major Japanese newspaper that the three companies had agreed on international division of labor on production of small cars in Seoul, said nothing definite has been decided.

The newspaper Nihon Keizai Shimbun reported that Mazda would be in charge of development of the subcompact cars, Kia would handle production of 120,000 units a year starting in 1987, and Ford would sell most of the cars in the United States.

Mazda would build a new auto plant costing between $200 million and $240 million, the paper said.

The Mazda spokesman did not deny that such an arrangement eventually would be reached, given the relationship of the three auto makers.

At present, Mazda has an 8 percent stake in the Seoul-based auto company and Ford owns about 25 percent of Mazda. Ford Chairman Donald Petersen has stated publicly that his company is ready to purchase subcompacts from Kia.