In mid-June U.S. Ambasssdor to Japan Mike Mansfield was informed that a Senate staff aide, in travels to Tokyo, had told Japanese officials that Mansfield was "not in touch" any longer with his former legislative home on Capitol Hill.

The angry Mansfield dispatched a six-page cable of complaint to one of his former colleagues, and the aide was summoned home from Asia and fired from his job.

Michael Pillsbury, a Republican staff assistant to the Senate Budget Committee until the arrival of Mansfield's cable, said yesterday that his outster was the result of "a series of misunderstandings" and "misquotations" by a U.S. embassy officer in Tokyo. He declined further comment pending additional developments in the case.

Pillsbury, an outspoken advocate of U.S - China military ties, was quoted by embassy officials in Tokyo as suggesting that Japan should beef up its armed strength. Mansfield reportedly took strong offense, saying that such statements contradicted U.S. policy and complicated the work of the embassy.

The case has attracted wide press attention in Japan, where U.S. views on rearmament are a sensitive matter. Some Japanese press accounts have portrayed Pillsbury's firing as part of a struggle over U.S. policy toward its senior Asian ally.

In the Senate, the case has been complicated by the fact that Mansfield and the old colleague whom he cabled, Chairman Edmund S. Muskie (D-Maine) of the Senate Budget Committee, are Democrats, while Pillsbury was an aide to Republican committee members.

The request for his resignation, according to Capitol Hill accounts, was handled at the staff level. Staff members of GOP senators were given three subsequent briefings on the subject by the GOP staff chief, Bob Boyd.

Pillsbury, 33, who was formerly an analyst for the Rand Corp. and had been with the Budget Committee only five months, stopped in Japan for four days in June after a three-week trip to China.

The discussions that caused the trouble took place between Pillsbury and officials of Japan's Foreign Ministry and Self-Defense Agency, and were attended by an embassy political officer who acted as the staffer's escort and interpreter.

The report on the conversations by the embassy officer, Robert McCallum, went to Mansfield's desk for clearance as a cable back to Washington. This prompted an immediate and explosive reaction from the former Senate majority leader from Montana.

Pillsbury, who had traveled on to South Korea for further discussions, was summarily called home and presented with Mansfield's protests. The aide gave his own and different version of events, but was asked to resign nevertheless.