PERHAPS THE ACTION of President Carter in freezing exports of American goods and technology intended for use at the Moscow Olympics will help get a simple message through to the more recalcitrant American athletes and organizers of international athletic events. The message is that American participation in the Games next summer is not in the best interest of the United States and won't be encouraged or assisted. As long as the Olympic hierarchy, here and abroad, and some of the athletes cling to the fantasy of American participation, moreover, planning for alternative events will lack the sense of urgency that alone can make them succeed.

The various suggestions of how American athletes could both participate and protest in Moscow reflect a failure to accept a truth that should have been clear weeks ago. Marching into the opening ceremonies behind the Olympic flag instead of the American flag, for instance, would be a joke. The symbolism of the gesture would be overwhelmed by the reality that the Americans, after all, were there.

The fact is that the Soviet Union vigorously sought an Olympics for Moscow to demonstrate that at last it has been fully accepted by the company of nations, just as West Germany sought an Olympics for Munich to demonstrate its return to international respectability. With success within reach, however, the Kremlin ordered its army into Afghanistan. The Russian bear, which in its cuddly form had been chosen as the symbol of the Summer Games, became, not for the first time, a cynical and brutal occupier. Once that was done, American participation at Moscow could only be interpreted as a public declaration that the United States cares less about such things than it does about having its athletes play their games. Having decided that Americans would not go to Moscow unless Soviet troops leave Afghanistan, the American government cannot reverse or relax its position without making a joke of its protests against the Soviet act.

That is what the American -- and the international -- sports world seems unable to grasp. It is not a matter of suddenly injecting politics into sports. Politics was the essence of the Soviet Union's demand to be an Olympic host and it has been near the heart of the modern Olympic Games for at least a half century. In fact, politics was there 2,000 years ago. The ancient Greeks conducted their Games on a four-year cycle -- at Olympia, Delphi, Isthmia and Nemea -- and the athletes from Elis did not compete at Isthmia because those Games were sponsored by Elis' arch-rival, Corinth. But you don't need all that Isthmia business to make the modern point: A boycott of Moscow, by the United States or any other nation, would not be an unseemly latter-day "political" intrusion. It would be the right thing to do.