The British Olympic committee made clear today its intention to participate in next summer's Olympics in Moscow, although it postponed formal acceptance of the invitation for three weeks.

In a damaging blow to the campaign by President Carter and British Prime Minister Margaret Thatcher for a boycott of the Moscow games to protest the Soviet invasion of Afghanistan, the British Committee confirmed "its present intention to send a British team to Moscow."

The committee's chairman, Dennis Follows, said there was little doubt Britain would formally accept its invitation on March 25, three days after British Olympic officials confer with representatives of other Western European Olympic committees in Brussels.

"It would have been impolite, injudicious perhaps," Follows said, "to take a firm decision without consultation."

But he emphasized that the overwhelming majority of the British committee's members, the heads of various sport organizations, strongly favored participating in the Moscow games and wanted this known to British athletes training for them and potential contributors of the funds to pay their way. Asked if the invitation would be accepted in three weeks, Follows added, "On the basis of what has been said today, the answer is yes."

Thatcher has been the only Western European leader to support Carter's Olympic boycott campaign publicly and unequivocally. But she also has said she would not try to force British athletes to stay home. "The government can only advise and people are free to make their own decisions," she repeated today in Parliament.

Other European governments have delayed taking a public stand on the Olympics both because they believe there is still time for the Soviets to indicate that they will withdraw their troops from Afghanistan and because they fear their national Olympic committees would decided to go to Moscow anyway.

A British attempt last month to persuade the other eight European Common Market countries to warn publicly that they may also ask their athletes to boycott the games was blocked by the French.

The Thatcher government worked up to the last minute to persuade the British Olympic Committee at least to delay its decision until nearer to the May 24 deadline.

But many British athletes had already made clear their determination to go to Moscow no matter what the government or even the British Olympic Committee says or does. British organizations for 14 of the 26 sports involved in the games had already indicated that they wanted Britain's invitation accepted.

The International Athletes' Club, composed of Britain's top track and field competitors, announced yesterday that it had decided to spend more than $100,000 to send its own team of 50 athletes to the games if the British Olympic Committee does not accept its invitation.