In an attempt to restore momentum to their sagging campaign for a boycott of next summer's Moscow Olympics, the United States, Britain and Australia are arranging a meeting of Western and nonaligned nations next week to decide whether they can stage alternative games for athletes who stay away from Moscow.

The hastily called meeting is tentatively scheduled for Monday and Tuesday in Geneva for an undetermined number of nations that agree to participate. It will come less than a week before representatives of Europe's national Olympic committees gather in Brussels on March 22 to discuss the issue. Most of them still appear ready to accept invitations to participate in the Moscow Games.

British government sources said U.S. British and Australian officials intend to explore next week the possibility of staging alternative games during the last two weeks in August at four or five sites scattered around the world, with four or five Olympic events held at each site. London, Los Angeles, Brisbane and Nairobi are reportedly among the potential sites to be offered.

"We will be seeking commitments on where alternative games can be held," said one British source. "We are aware of the difficulties of athletes who have trained all their carreers for the Olympics. We want to give them an alternative competition of comparable standards and media coverage.We want to give them their chance to shine."

Until now, governments interested in the idea of alternative games have been unable to get much information from the Carter adminstration on its intentions or on the feasibility of sites for such games. Next week's meeting is timed, one source here acknowledged, to try to influence nations and national Olympic committees "who are now on the fence" to join in a boycott of the Moscow Games.

But the Campaign to stay away from Moscow to protect the Soviet invasion of Afghanistan has already lost some steam. Canada, for example, an outspoken proponent of a boycott before Pierre Trudeau replaced Joe Clark as prime minister, is conspicuously absent from among the organizers of next week's meeting.

Most Western European countries have postponed a decision on the Moscow games until nearer the deadline in May for acceptance of invitations by their Olympic committees, which might well go their own way in any event. Attempts to put the nine European Common Market nations formally on the record as threatening to advise their athletes to boycott the Olympics if Soviet troops are not withdrawn from Afghanistan have been blocked by France.

Even the British government of Prime Minister Margaret Thatcher, the only one in Europe to publicly support the boycott, has been unable to persuade the British Olympic Committee to follow its lead. The government has increased the pressure on athletes by refusing leave to government employes who want to compete in Moscow and by scheduling a parliamentary debate and nonbinding vote on the issue next week.

But these moves could backfire on Thatcher's government. There is no assurance that it will win the vote in the House of Commons, for which members have been freed of binding party instructions. British Olympic officials and athletes, meanwhile, have emphasized their determination to go to Moscow if it remains legally and politically possible.

Sir Dennis Follows, chairman of the British Olympic Committee, complained that the Commons debate and vote "could seriously affect the liberty of the British subject in peacetime. There is, in effect, a war mentality prevailing at the moment with sportsmen being used as shock troops."

Emphasizing the independence of sports officials in Britain, he said their "position remains the same. The government . . . does not want a British contingent at the Olympic Games, but for the most part the governing bodies concerned and the potential competitors want to compete."

One of the stars among the potential competitors, world mile record holder Sebastian Coe, said today he will compete in Moscow unless the British Olympic Committee refused its invitaton.

"I believe it was all thought up by President Carter's election bandwagon," said Dick Palmer, the secretary of the British Olympic Committee. "Britain's athletes will be left after eight years' hard work as forgotten people.