The three largest Silicon Valley semiconductor manufacturers yesterday accused their major Japanese competitors of dumping chips at prices below manufacturing costs to capture a large share of the American market.

The three companies -- Advanced Micro Devices Inc., Intel Corp. and National Semiconductor Corp. -- asked the U. S. International Trade Commission and the Commerce Department to impose penalty duties that in some cases are higher than the present cost of the chips.

This is the third major unfair trade case filed against Japan in recent months by segments of the U.S. semiconductor industry, which has been financially battered by an unexpected slowdown in computer sales as well as strong competition in this country and overseas from aggressive Japanese manufacturers.

In the dumping case, the American companies accused the eight Japanese makers of EPROMS (erasable programmable read-only memories), a kind of semiconductor memory device used to store programs, of dumping chips, which is illegal under U.S. law. The eight companies, which include some of the giants of Japan's high-technology industry, are Fujitsu Ltd., Hitachi Ltd., Matsushita Electric Corp., Mitsubishi Corp., NEC Corp., Oki Ltd., Ricoh Corp. and Toshiba Ltd.

F. Thomas Dunlap, general counsel for Intel, said the Japanese companies are "committed to gaining market share at any cost. They can afford to engage in predatory pricing because they are part of giant Japanese conglomerates prepared to subsidize their semiconductor operations for as long as it takes to get control of the market."

The trade complaint cites a memo from Hitachi that exhorts its U.S. distributers "to win with the 10 percent rule" by continually cutting prices. Find the U.S. companies' price, the memo says, and "quote 10 percent below their price. If they requote, go 10 percent again. Don't quit until you win."

According to the domestic manufacturers, one type of EPROM cost $17 each in January, when Japan aggressively entered the U.S. market. By August, the price had dropped to $4 even though the U.S. manufacturers estimated it cost the Japanese companies $6.34 to make the chip. The price of another form of the chip dropped from $7.50 to under $4.

As a result, Japan captured 60 percent of the U.S. market despite what the domestic makers said is their technological and marketing superiority. "We have invested heavily in new plants and equipment and have proven ourselves vigorous competitors in the $1.1 billion worldwide EPROM market," Dunlap said.

In June, the Semiconductor Industry of America charged in a petition to the U.S. Trade Representative that they were illegally denied full access to Japan's market. The industry in that case cited statistics showing that U.S. makers held 5 percent of the European chip market, but could get no more than 11 percent of the market in Japan.

R. Michael Gadbaw, who filed the dumping complaint for the three chip makers, said the two trade complaints together explain the Japanese strategy for gaining dominance in high technology by protecting its home market from foreign competitors and dumping chips overseas to win those markets.

In dumping cases, the ITC determines whether a U.S. company has been hurt, while the Commerce Department rules whether illegal dumping has taken place.