TOKYO, JULY 14 -- Prime Minister Yasuhiro Nakasone called Toshiba Machine Co.'s illegal sales of high technology to the Soviets a "betrayal" against the Japanese people today shortly before his envoy, Japan's trade minister, departed to face American anger over the incident.

The prime minister, speaking during a nationally televised question-and-answer session with opposition members in the Diet (legislature), said the sales were "made illegally and systematically through false applications."

"It is a grave act of betrayal not only to the United States and other countries, but also to the Japanese people," Nakasone said of the sales of the propeller-milling machines, which help make Soviet submarines quieter and harder to detect.

He said the firm's actions dealt a blow to the nation's defense, which is paid for by Japanese taxpayers.

Toshiba Machine, owned 50.1 percent by giant electronics firm Toshiba Corp., is accused of selling $17 million in propeller-milling machinery to the Soviets from 1982 to 1984 in violation of Japanese and international export control laws.

Nakasone said the government was studying measures, including extending the statute of limitations on Japan's export control laws, to prevent further incidents, and investigating whether other Japanese firms have made similar sales.

In Washington, Japanese trade minister Hajime Tamura is expected to brief U.S. officials on new preventive measures Japan plans to take in the wake of the Toshiba sales as he attempts to defuse tension over the affair.

Ministry of Trade and Industry officials said Tamura left for Washington today on a six-day visit.

An official, who refused to be identified, said Tamura is to meet with U.S. Secretary of Defense Caspar Weinberger, Sen. Daniel J. Evans (R-Wash.) and presidential adviser Frank Carlucci on Wednesday.

He is scheduled to meet with Secretary of Commerce Malcolm Baldrige on Thursday, and with U.S. Trade Representative Clayton Yeutter on Friday