The semi-collapse of the Olympic boycott signals the beginning of the end of the Afghan round in the world politics. The United States has suffered a shattering loss. The Russians have scored a sweeping strategic gain.

To be sure, the invasion of Afghanistan carried costs. The Russians absorbed heavy casualties, and still face sporadic resistance in outlying areas. But Soviet troops have cracked down hard, killing thousands of Afghans, and driving perhaps a million -- out of a population of 18 million -- into exile.

Now Moscow is moving to legitimize the conquest. On May 14 the puppet government in Kabul issued a call for talks with Iran and Pakistan to "normalize relations" on the basis of no outside interference in Afghan affairs and the cessation of "military and politically activity in the Indian Ocean and Persian Gulf area by states which do not belong to that area." In other words, the communists proposed that the United States withdraw from the Persian Gulf and the Indian Ocean. In return the communists offered to "resolve the question of withdrawal from Afghanistan territory of the Soviet limited military contingent."

On May 15, the Russians gave that appeal their approval in a statement from the meetng of the Warsaw Pact countries. The Warsaw Pact statement added to the appeal for acceptance of the puppet regime in Kabul a mixture ot threat and promise on detente with Western Europe. The Russians offered to resume talks on arms control, but threatened an intensification of pressure if the West Europeans did not drop projected plans for modernization of NATO forces.

On May 16 the new secretary of state, Edmund Muskie, met with Soviet Foreign Minister Andrei Gromyko in Vienna. Muskie emphasized continued American dissatisfaction with the Soviet move into Afghanistan. But he also indicated that at bottom the United States wanted to resume detente with Moscow.

That was all the Europeans needed. An implicit break with the United States on how to balance ties with Moscow against interests in the Middle East and Persian Gulf burst into the open. French President Valery Giscard d'Estaing met with Leonid Brezhnev in Warsaw without even giving the United States advance notice. Chancellor Helmut Schmidt of West Germany is off to Moscow for talks with Rezhnev in July. The British have been talking for months about a deal to achieve the "neutralization" of Afghanistan. It is only a matter of time -- and not much time -- before the Europeans forget Afghanistan and go back to business as usual with the Russians.

The Islamic world has proved no more more prone to stick with the United States than the Russians. Immediately after the invasion of Afghanistan, the Carter doctrine was proclaimed to draw the line against any further Soviet advances. An offer of military assistance was rushed to Pakistan, and the president spoke of pitting "militant Islam" against "atheistic communism."

At a meeting of the Islamic Conference in Pakistan at the end of January, 34 Moslem countries condemned "the Soviet militaryy aggression against the Afghan people." But subsequently Pakistan rejected Washington's offer of military assistance as "peanuts." The abortive American effort to rescue the hostages drove Iran into a frenzy of hatred and obliged most other Moslem countries to denounce Washington.

At another meeting the Islamic Conference in Pakistan last week, the gravamen of condemnation was directed against the United States. The conference designated a committee of two -- Pakistan and Iran -- to explore the peace offer of the Afghan regime. It seems not at all unlikely that in the near future, the Iranians and Pakistanis will signal their final withdrawal from the Western orbit by doing a deal that in effect recognized Moscow's predominance in Southwest Asia.

What follows in that area remains obscure. Certainly the Russians now have no fear of massive aid to the Afghan rebels. Nor any challenge from Pakistan or Iran. After digesting Afghanistan, Moscow will be in good position to pick up the pieces as the various divisive forces work their way in the area. Moreover the dismal U.S. record in the region is eventually bound to make the Chinese reassess their decision to switch from dependence upon Russia to dependence upon the United States.

So the outcome of the Afghan round is not merely another country under Moscow's heel. The Russians have also driven a wedge between the United States and its European allies. They have fostered a mood of neutralist acquiescence in Southwest Asia. They have raised the possibility that the so-called China card might eventually end up in the hand of Moscow.