U.S. semiconductor companies formally sought trade relief yesterday by charging their Japanese counterparts with illegally forcing the price of microchips down in this country while barring American producers from the Japanese market.

"We seek a more responsible and responsive attitude and effective actions in Japan to expeditiously deal with these problems. We do not seek a trade war; we are trying to avoid one," said Gary Tooker, chairman of the Semiconductor Industry Association, which represents virtually all of the nation's independent manufacturers of silicon chips.

The SIA filed an action with the U.S. Trade Representative's Office under Section 301 of the 1974 Trade Act, which allows the president to retaliate against nations alleged to have unjustifiable or discriminatory trade practices. The trade representative has 45 days to decide whether to hear the action.

But Japanese representatives claimed such actions were unwarranted. "The Japanese semiconductor market, along with that of the United States, is the most open market in the world, offering free access to trade and investment," said Akio Morita, chairman of the Electronic Industries Association of Japan and chairman of Sony. He added that he believes there is "no basis" for the allegations of the American manufacturers.

Complaining bitterly that Japanese companies, specifically Hitachi, are "dumping" their semiconductor microchips -- that is, selling them at prices below cost in an effort to drive American firms out of business -- George Scalise, chairman of SIA's public policy committee, pointed to a memo he said was distributed by Hitachi in February.

The memo instructed employes on a "10 percent" rule: No matter how low the price quoted by the competition, quote 10 percent less. Microchip prices have been spiralling downward -- from well over $150 apiece to just a few dollars each, in some cases, although SIA would not quote specific figures.

According to figures from Dataquest Inc., a market research company in San Jose, Calif., Japan's share in the market for microchips that store information has grown from 22 percent of a $2.4 billion market in 1980 to 52 percent of a $6.5 billion market in 1984. SIA estimates the total semiconductor world market as $26 billion in 1984, with the United States' share 54 percent and Japan's 37 percent. Last year's sales were estimated at $11.6 billion in the United States and $7 billion in Japan.

While Japan's market share in this country has grown over the years, American manufacturers claim that their share in Japan's market has remained about 11 percent in recent years. Hidehiro Konno, Japan's counselor for commercial affairs, claimed that the United States' market share in his country is actually 19 percent, once the market share of Japanese branches of American firms is taken into consideration.

Konno said that the United States "is afraid that Japanese companies are expanding their capacity very rapidly. The fact is, Japanese companies are expected to reduce their fixed investment." He also projects a decline of 15 percent in investment in semiconductors in Japan, compared with projected growth of more than 40 percent in investment in semiconductors in the United States.

Experts in the industry are quick to praise Japanese products and organization, pointing out that Japanese firms have more flexibility to extend funds for research and development projects. "The market plays into the Japanese strengths. They don't shortchange their research and development," said Dataquest senior industry analyst Lane Mason, who is a specialist in the semiconductor memory market.

Richard A. Shaffer, who edits and publishes Computer Letter, said that superior technology delivers Japan's market share. "I think in memory circuit, it's all over," he said. "It gives me the feeling you would have had living in 19th-century England, watching America take over."

American manufacturors, though, are nervous, fearing that, if the Japanese continue to sell semiconductors at such a great rate, U.S. firms soon will be out of business or facing severe cutbacks. The three members of the House of Representatives from the Silicon Valley area of California are circulating a letter among that state's congressmen, seeking support for the action.

"It doesn't add up -- how we're doing in Japan. The only answer is that they're being anticompetitive," said Rep. Don Edwards (D-Calif.). "We want the Japanese to get the message right now."

The SIA is contemplating other action, including a possible antitrust-violation charge, according to Scalise. "We're looking into a whole gamut available to use," he said. SIA is not asking for short-term quotas or trade embargoes because the group perceives the problem as ongoing, he said.

"The semiconductor industry in America is currently suffering from a deep recession. Nationwide, as many as 20,000 jobs have been lost, many of which can be traced directly both to market barriers in Japan and possibly predatory pricing," said Sen. Pete Wilson (R-Calif.).