Prime Minister Pierre Trudeau's government today announced its firm opposition to Canada's participation in the Moscow Summer Olympics, calling the boycott "the clearest and most effective way available" to condemn the Soviet invasion of Afghanistan.

The announcement, made on the eve of a visit Wednesday by Secretary of State Cyrus Vance, removed doubts about Trudeau's position and virtually enusred that the Canadian national team would not go to Moscow next summer.

[In Lausanne, Switzerland, a proposal before the International Olympic Committee to allow individuals to participate in the Moscow Games even if their governments did not seemed doomed after it failed to win the support of the committee president, Lord Killanin].

[Killanin said the proposal would undermine the national Olympic committees and would involve a considerable change in the Olympic rules, which would be difficult to do in time for the Moscow Games, Washington Post special correspondent Anne Crosman reported.]

With its announcement, Canada joins major U.S. allies Japan, Australia, Britian and West Germany in recommending that their Olympic committees follow the U.S.-led boycott.

While the Canadian Olympic Association is scheduled to make a final decision at a meeting in Montreal Friday, its president Dick Pound said that a majority of association leaders "are in favor of not going" to Moscow.

The announcement was apparently timed to avoid the impression that the Canadians are being forced by Vance to follow the American lead. It also coincides with what Canadian officials described as a developing "tidal wave" that President Carter has been seeking since he announced the boycott effort Jan. 20.

Carter's announcement was made in the middle of Canada's election campaign and was promptly endorsed by the then-incumbent Conservative prime minister Joe Clark. At the time Trudeau voiced reservations about the boycott and said he would favor it only if a majority of the countries, including Third World countries, were to participate to make it effective.

Reading the announcement in the House of Commons today, External Affairs Minister Mark MacGuigan said that Canada has consulted with a number of Western and Third World countries in the past three weeks and that "we are convinced that the criteria for an effective boycott are now clearly present."

To ask Canadian athletes to forego Moscow Games, MacGuigan said, "is a hard thing for any free country to ask of its citizens.

"The government is, however, convinced that withdrawing from the Olympics is the clearest and most effective way available to make plain to the leaders of the Soviet Union that the world condemns the Soviet invasion of Afghanistan and its defiance of international demands for its withdrawal.

"The government believes that the international situation brought about by the Soviet invasion of Afghanistan makes it wholly inapproprate to hold the Olympic Games in Moscow."

MacGuigan said that the government would support Canadian athletes wishing to participate in alternate games, and Sports Minister Gerald Regan said that the possibility of utilizing some existing facilities in different regions of this country" is being considered.

Correspondent Crosman also reported from Lausanne:

The IOC executive board continued its meetings to discuss the worsening situation of the Moscow Games now that the U.S. boycott is getting more support and fewer countries are planning to send athletes to Moscow.

Lord Killanin also played down a proposal to eliminate flags, anthems and ceremonies from the Moscow Games.

"Any changes in protocal would need a majority vote by the IOC as a whole," he said. The next full IOC session is scheduled for Moscow in July, but another one could be called sooner. "I just don't know what we'll do about this," Killanin told reporters.

MacGuigan said the government would not resort to cohersive measures against Canadian athletes and he ruled out any form of travel restrictions.

He appealed, however, both to the Canadian Olympic Association and to individual athletes to support the decision and to make the "sacrifices" asked of them.

MacGuigan also indicated that several foreign ministers have informed him in conversations during the Zimbabwean independence celebration last week that they would join the boycott.

"I expect more such announcements in the coming days." he added.

Canadian sources said that Trudeau had approved the boycott reluctantly, in large part because it meant a partial reversal of his earlier public position. They also said Ottawa was subjected to considerable American pressure and that they have come to realize that failure to support Carter on this issue would have made future dealings with his administration very difficult.

According to this view, Carter has made the allied support of the boycott a kind of loyalty test.

Afghanistan and Iran are scheduled to be discussed Wednesday by Trudeau, MacGuigan and Vance. Vance's trip here is seen as part of U.S. efforts to solidify allied support for Carter's post-Afghanistan policies.