United Auto Workers President Douglas Fraser claimed today that Toyota Motor Co. has changed its position and is giving "serious consideration" to building a manufacturing plant in the United States.

He said he based that assessment on a conversation today with Eiji Toyoda the company's president.

However, a spokesman for the company said he knew nothing of any change in its plans and put out a version of Toyoda's remarks to Fraser that contained no indication of any change.

(In Washington, meanwhile, the Labor Department, in its largest foreign trade investigation ever, said it would determine whether 200,000 auto workers are entitled to special federal unemployment benefits because of import competition.)

The conflicting accounts in Japan left some confusion in the wake of Fraser's visit to Japan's big automakers this week, but the sum of it was that no hard promises were made by anyone.

Fraser spent four days talking with industry leaders and government representatives, calling in them to have Japanese companies open plants in the United States and warning that, if they don't, congress will pass legislation restricting imports of cars made in Japan.

Yesterday, after meeting with executives of Nissan Motor co., Fraser had said he was disappointed to find they only would discuss the possibility of making trucks, not cars, in the United States and giving several reasons why making cars might not be profitable there.

But today, Fraser said he left the Toyota meeting "with some encouragement" because the company president had appeared to change his mind. "He told us that because changing events. Toyota is giving serious consideration to locating a plant in the United States," Fraser said.

Fraser said he asked Toyoda if that represented a change in his position and the answer was "Yes." Later, referring to notes, he quoted Toyoda as saying: "Events have caused us to take a more serious look at locating in the United States."

On Wednesday, citing U.S. industry sources, The Washington Post reported that Toyota was expected to announce plans for a U.S. plant in the wake of Fraser's visit. And today, the union leader said Toyoda authorized him to tell Congress that the company's position has changed. But Toyota's public relations department quickly issued a statement that quoted Toyoda as saying only that any decision to build a plant there "must be treated with great care."

Toyota has made extensive surveys recently in the United States and is thought to be on the verge of making an announcement quickly, but there are conflicting views on what that decision will be.

Recent stories in the Japanese press have suggested its answer will be negative. One recent report indicated that Toyota will answer American criticism by restraining its exports to the United States rather than build a plant in that country.

Both Toyota and Nissan, the No. 2 automaker, have clearly stated they doubt the economic feasibility of a U.S. plant, but they are being pressured by the government to build plants anywhere to reduce frictions between the two countries.

This government pressure was underscored by Fraser today when he said that his meetings with government officials had been excellent. He quoted Takeshi Yasukawa, the foreign ministry's top trade adviser, as promising to advocate the construction of Japanese plants in the United States.

So far, Honda Motor Co. has announced it will start building 10,000 cars a month in an Ohio plant but neither Nissan nor Toyota have made any commitments.

Foreign imports accounted for about 22 percent of all auto sales in the United States. Last year, and about three out of every four of those foreign sales was made by a Japanese firm. Sales of Japanese-made cars soared again in Januray.

The U.S. Labor Department said its investigation involves employes of General Motors Corp. and Ford Motor Co. at 149 facilities around the country.

Under-the Trade Act of 1974, American workers who lose their jobs or face job cuts because of increased sales of imports in their industry are entitled to special benefits that include 70 percent of their weekly pay for up to a year and special job training and relocation services.