Canada has ordered the expulsion of two Soviet military attaches and an embassy chauffeur for espionage that involved buying U.S. secrets from an American "in a sensitive position," External Affairs Minister Flora MacDonald announced today.

MacDonald refused to reveal the American's identity or the nature of the information involved.

She said the American was neither a military man nor a civil servant, but was "in the kind of establishment that would have been utilized by the government."

He "helped" the Federal Bureau of Investigation, which assisted Canadian authorities in the probe that was completed last week, MacDonald said. She said it would be up to U.S. authorities to determine if any action would be taken against the American.

[FBI and State Department officials in Washington also refused to identify the American or to say whether any further action was likely in the United States.]

The action against the Soviet officials followed the expulsion of 13 staff members of the Soviet Embassy nearly two years ago, when Canada sharply warned Moscow against further espionage out of its Ottawa embassy.

The three ordered expelled today were Capt. Igor A. Bardeey, military, naval and air attache; Col. Eduard Aleksanian, assistant military attache, and V. I. Sokolov, a chauffeur.

A Soviet Embassy spokesman denied that the attaches and chaffeur were spies and suggested that the expulsions were linked to Western protests of the Soviet military intervention in Afghanistan. MacDonald said there was no connection.

MacDonald said the case involved an American "employed in a sensitive position in his own country, who was in contact with the Soviet Embassy in Ottawa and was paid by the embassy to obtain classified information."

She said the Soviets had paid more than $100,000. Over a period of 16 months, she said, the Soviets "met clandestinely with the U.S. citizen, using traditional signal arrangements and dead-letter boxes in the Ottawa area, where exchanges of information took place and payments were made."

It was not clear from the statement whether the American had assisted authorities from the outset or had been apprehended and persuaded to work against the Soviets. MacDonald said Canadian officials had uncovered the affair.

Meanwhile, Japanese officials said today that an unrelated espionage case there might expand to include more arrests of Japanese military officers, in addition to three charged last week.

That case, according to officials in Tokyo, involves leaking of Japanese information on China to Soviet agents. U.S. military secrets were not involved, Japanese officials said.