Toyota Motor Co., Japan's largest auto manufacturer and the No. 3 American seller in January (displacing Chrysler Corp.), may announce plans in the near future for construction of an automobile assembly plant in this country.

According to industry sources, a visit this week to Japan by United Auto Workers President Douglas Fraser is the key element in helping to convince the company's management that it must begin to manufacture cars here or be confronted with some type of import restrictions.

Significantly, a Japanese governmentofficial urged his country's auto firms yesterday to curb exports to the U. S. voluntarily and start production in this country in order to ease trade friction between the two nations.

Quoting an unidentified official at the Ministry of International Trade and Industry, Dow Jones News Service reported from Tokyo that the government told both Toyota and Nissan Motor Co. about its policy in a series of meetings before Fraser's arrival. Nissan, which builds Datsuns, is the second largest of Japan's auto firms.

"Of course, they have to think about a lot of things . . . whether they can acquire necessary parts in the U.S., the labor situation in the U.S. and Japan as well as distribution systems. . . nevertheless, it's the government's position to encourage production in the U.S.," the official stated.

Honda, a maverick in the Japanese industry, already has announced plans to build 10,000 cars a month at an Ohio assembly plant by 1982. But spokesman for Japan's largest firms have said consistently that they have no such plans for now, although production plants are planned later in this decade.

As sales of Japanese-made cars have surged in recent months, the traditionally free-trade auto industry has become divided on the question of import controls and pressure is growing for establishment of trade restrictions.

At a news conference yesterday in Nagoya, Japan, Toyota President Eiji Toyoda said his company has dispatched a survey team to the U.S. but has no immediate plans to produce cars here. Other sources said they expect an announcement about Toyota production plans in the wake of Fraser's trip. Toyota also has been seeking Americans' advice on whether -- in the meantime -- to restrict exports here voluntarily, the source added.

Nissan President Takashi Ishihara told Fraser yesterday that his firm is "still unable to decide" whether to build cars in this country but that it would "exercise prudency" in exports, Nissan officials said.

Fraser is scheduled to meet Prime Minister Masayoshi Ohira and Foreign Minister Saburo Okita today to brief the Japanese leaders on the import issue. According to Nissan officials, Fraser yesterday pointed out that more than 200,000 U.S. auto workers currently are laid off and that "this is the election year . . . and people tend to become emotional."

The UAW chief has called on Japanese firms to reduce their share of the U.S. market to 17.5 percent, compared with 22 percent last month.

Toyota reported yesterday that its profits rose 53 1/2 percent in the six months ended Dec. 31 as sales volume was up 14 1/2 percent. Passenger car sales rose 79,000 to 1.07 million unis; exports soared to 490,568 from 120,201 units.

Separately, Volkswagen of America officials said yesterday they are considering only Sterling Heights, Mich., near Detroit, as the site for a second U.S. car assembly plant. An Army missile plant, where production ends later this year, would be used by VW. The plant would open late in 1982 and employ 4,000 persons within two years.