The United States, fighting to regain semiconductor sales lost to the Japanese, is pressing Tokyo to open its market to American high technology companies, U.S. Trade Representative William E. Brock told Congress's Joint Economic Committee yesterday.

"Our objective is to implement a mutually acceptable program for import promotion by Japan in November of this year," Brock said at a hearing on how targeting efforts by other countries damage America's ability to sell products at home and overseas.

The Semiconductor Industry Association is prepared to file an unfair trade practices case against Japan, attacking protectionist measures that have kept U.S. high-tech firms out of Japan. The industry will demand that American companies be allowed to sell more semiconductors to Japan, industry sources said. Filing of the formal complaint has been delayed to see if negotiations can produce the same result.

Brock never mentioned the threatened trade case, but said the government presented Japanese representatives earlier this month "with a series of proposals for the promotion of foreign semiconductor exports to Japan.

"The Japanese agreed to consider these proposals and possibly generate additional ideas of their own on improving access to the Japanese market."

Brock said Japanese government efforts--including direct financial aid, tax incentives, market protection from foreign imports and industry-government coordination--drove American companies out of Japan's market. By last year, a perennial U.S. trade surplus in semiconductor sales to Japan had turned into a $400 million deficit.

"In effect," said Brock, "Japanese companies that once trailed U.S. firms in RAM random access memory, the part of a computer that allows information to be stored and retrieved production and technology are now ahead."

Industry figures show that American companies had just 9.7 percent of the Japanese semiconductor market last year, despite a superior product, because of a "buy national" practice in Japan.

Yesterday's hearing, run by Sen. Lloyd Bentsen (D-Tex.), gets to what many experts believe is the heart of the trade disputes between the United States and Japan--industrial targeting by the Japanese government aimed at winning a predominant share of the American market.

Recent American moves against targeting practices have upset Japanese officials, who insist their industrial policies are strictly for internal economic development and not designed to capture overseas markets from American competitors.

But some American participants in United States-Japanese trade talks have not been persuaded. "Japanese officials are trying to explain what they do in a way that appears harmless. But what they think is harmless is actually aggressive, which makes you wonder," said one administration official who has taken part in the talks.

In a separate trade development yesterday, the Commerce Department ruled that China has been selling printcloth in the United States at 22 percent below its fair value, United Press International reported.

It was the first "dumping" case involving China to reach the stage of a final Commerce Department determination.

The announcement came on the day U.S. and Chinese officials resumed negotiations that have taken place off and on since February to renew the U.S. quota limiting the volume of textiles China may ship to this country.

Lawrence Brady, assistant commerce secretary for trade administration, said timing was a coincidence. The printcloth case grew out of a petition filed by the American Textile Manufacturers Institute last August. Such cases are governed by rigid deadlines.

Printcloth is a blend of cotton and polyester with nothing printed on it but which is ready for dyeing or printing. The ruling means importers of this product from China must make cash deposits or post bonds equal to 22.4 percent of the average price for each new shipment.