Three months ago, when the Soviet invasion Afghanistan was still a fresh taste, President Carter proposed a boycott of the 1980 summer Olympics in Moscow. The Canadian and British governments quickly agreed; West Germany and Japan signaled a willingness to go along; for a while, it looked as though the Moscow Olympics would collapse.

But in these hyperactive times, three months can change the world. There is a new Canadian government, one not interested in promoting an Olympic boycott. In Britain, the national Olympic committee has defied the government and decided to go to Moscow. The Japanese have let it be known that they don't want to be all along on this one. Even American athletes have begun to lobby against their president, many of them hoping to find a way to defy him and take part in the Moscow Olympics.

For President Carter, the Olympic boycott has been a characteristic undertaking. As he has done so often, on other issues -- the moral equivalent of war, for example -- the president has declared his position starkly, made a few public statements defending it, and otherwise dropped the issue, leaving the boycott effort to his staff. Members of his staff insist privately that the boycott will still be a success and that a substantial number of countries will in the end stay away from Moscow, but at the moment any confident predictions seem premature.

Meanwhile, curiously, the symbolic importance of the Olympic boycott has grown substantially, a point that is not mentioned in the continuing public debate on the question.

When the idea of a boycott was first broached, it was a novelty, almost a curiosity. Three months later, it is a major international issue, and the outcome of the American-led attempts to ruin the Moscow Olympiad will be seen throughtout the world as an important symbol of the international balance of power.

Opponents of a boycott may regard this transformation of this issue as unfair, but it is indisputable, nevertheless. The president of the United States has made the boycott a matter of superpower confrontation. The Soviets have taken up his challenge. They are sending emissaries around the world to drum up participants for the Olympics. In some countries -- Bolivia, Mauritius, Guinea-Bissau and others, according to the state Department -- the Russians have offered to help finance Olympic teams if they will just come to Moscow. The Soviet minister of sports is going to Japan to argue for an Olympic participation. Soviet Olympic officials are even touring the United States, arguing that the American team should be allowed to come to Moscow. If the Soviets win this contest, the rest of the world and the coming generation of Soviet leaders will surely know how to interpret the results.

If some way could have been found to avoid raising the issue, the 1980 Olympics might have been held in Moscow as planned without creating an impression that participating countries were somehow endorsing or at least accepting the Soviet invasion of Afghanistan. But this was never a real possibility, because The Soviets themselves were bound to raise the issue. In effect, they already have, declaring before the invasion that Moscow's selection as the site of the Olympics represented international recognition of the Soviet's peaceful foreign policy.

American proponents of the U.S. participation in these Olympics now are arguing, in effect, that President Carter deserves to be humiliated on this one. He overreacted, they argue, by volunteering to sacrifice the Olympics to the gods that preside over the superpower rivalry. Our games are more important than your games, the anti-boycott forces seem to be telling the politicians. Of course this is true for the athletes who have spent years, even lifetimes, preparing to compete in the 1980 Olympics. But can it be argued seriously by anyone else? In a world whose actual survival depends on successful management of the superpower rivalry, surely the politicians' games must take precedence.

Decisions by American athletic officials that either frustrate the president's international boycott coampaign or make possible some kind of American participation in Moscow are unlikely to be described in future histories of these weird times as mere humiliations of President Carter. They would be much more significant than that.

There may be no more important question before America and the world than this: can the United States run its end of the superpower confrontation with strength, confidence and common sense? If it cannot, the last years of the 20th century are going to be grim. Decisions taken by American athletic officials this spring that undermine American policy toward this misbegotten Olympiad would diminish the prospects for a happier outcome.