U.S. Ambassador Mike Mansfield warned yesterday that Japan's continuing high trade surpluses may trigger a revival of restrictive legislation in the U.S. Congress that would hurt Japanese commercial interests.

Mansfield pointed to Japan's "expluses in early months of this year and extremely high" current account sur-said they had "imposed heavy burdens' on other countries.

"This situation should be reversed," the ambassador said in a speech to business groups meeting in the industrial city of Osaka.

"If it does not begin to improve soon, Congress will, in all likelihood, begin to lose patience and may well consider legislation which hurts trade and the economic interests of all trading nations, especially Japan," he added.

His unusually pointed comments came at a time of renewed doubt that the measures Japan has planned so far will do much to reduce its trade surplus with the United States.

Three mlnths ago, the two countries reached agreement on a general approach to reducing that surplus. Although both sides acknowledge that that plan will require time to take effect, the trend so far has not been promising.

Japan's exports have continued to boom along while there has been no discernible sign that imports of U.S. and other foreign products will increase in the near future. It is now expected that the current accounts surplus for the fiscal year that ended last week may exceed $13 billion.

In February alone, the current account was in surplus by $1.8 million, nearly three times that of February, 1977.

Moreover, recent indicators project continued increases.

Some Japanese officials have suggested in the past week that it is time to invoke a mandatory export-control law to prevent the country's surplus from soaring even higher and alienating the United States and Europe further. Their advice is opposed by the powerful Ministry of International Trade and Industry, which insists that strict controls would wreck the Japanese economy.

Mansfield disagreed with the frequent Japanese assertion that the trade inbalance is mainly due to the large U.S. importation of foreign oil. Oil is a factor, he said, but it is not the source of the greatest danger to trade between the two countries.

"The danger," he said, "lies in the widely held belief in the U.S. of an economic imbalance of opportunity in our bilateral trade.

"Japan's remaining import restrictions, its rising exports, and the problems American manufacturers have in selling their products here have brought about the serious situation in the American Congress."

The ambassador praised Japan for promising to lower import tariffs during the current negotiations in Geneva and for announcing some reductions earlier than resuired. The United States is "not completely satisfied" with the proposed reductions, "but we are moving in the right direction," he said.

Both countries, he added, must have an equal opportunity to sell in the other's markets.

"If Americans have the same access into your market that you have in ours and still cannot compete successfully or balance our bilateral trade, then the blame for that inbalance will fall squarely upon the U.S., its manufacturers, and its exporters," Mansfield said.

"But as long as any inequality or unfair restrictions continue to exists, then Japan will continue to be partially blamed - fairly or unfairly - for our trade imbalance. Those are the facts of political life."

He said: "The time has come to demonstrate your complete and open commitment to free trade by allowing others access to your market."

The ambassador's speech was delivered to a joint meeting in the Osaka Chamber of Commerce and Industry, the Kansai Committee for Economic Development, the Kansai Economic Federation, the U.S.-Japan Society and the American Chamber of Commercee in Japan.