Toyota Motor Corp., Japan's largest auto maker, tentatively has chosen a small Kentucky college town as the site for its own assembly plant in the United States.

Sources familiar with the company's decision said that Toyota officials, led by company President Shoichiro Toyoda, will make the announcement in the United States next Wednesday.

Toyota already has the capacity to produce nearly 250,000 small cars a year in this country through New United Motor Manufacturing Corp., a joint-venture company equally shared with General Motors Corp., in Fremont, Calif. NUMMI produces subcompact Nova passenger cars.

The independently owned Toyota site will be in Georgetown, Ky., a town of about 10,000 people, located in the central portion of the state. Georgetown is the home of Georgetown College, a small Baptist institution. Toyota is expected to produce 200,000 cars a year at the new plant.

Toyota announced July 23 that it will start building cars on its own in the United States. The announcement did not come as a surprise.

Japanese auto makers have been laboring under "voluntary" import quotas since April 1, 1981. Those restrictions initially held their shipments to the American market down to an official limit of 1.68 million cars a year. That ceiling eventually was lifted to 1.85 million units, and last year was placed at nearly 2.4 million cars a year.

Japanese auto makers who already had a foothold in the United States profited greatly as a result of those restrictions -- they could charge higher prices because of limited product availability.

But the Japanese feared that they would lose the more important battle for U.S. market share if they could not get around the quotas, or if they were forced, because of growing protectionist sentiments in this country, to work under even more severe restrictions.

An alternative route to greater market share was to build the cars where they are sold.

Honda Motor Co. was the first Japanese company to choose that route, when it started building Honda Accord sedans in the United States in 1982. Honda since has embarked on a $240 million expansion of its American facilities, which would give the company the capacity to assemble nearly 300,000 cars a year by 1987.

Honda officials told The Washington Post last month that they are considering adding another U.S. plant to assemble an additional 100,000 cars annually.

Mazda Motor Corp. plans to start building 240,000 cars a year in Flat Rock, Mich., by 1988. About half of that production is expected to go to Ford Motor Co., which owns about 15 percent of Mazda.

Mitsubishi Motors Corp. this year said that it will build cars with Chrysler Motor Corp. in an Illinois joint-venture company called Diamond-Star Motors. Nissan Motor Co. Ltd. is building subcompact cars and trucks in Smyrna, Tenn.