THE MORE YOU think about it, more fantastic it seems that the cream of the Soviet cultural elite keep renouncing their homes, privileges and comrades in the Soviet Union and defecting to the West. Year after year they arrive; no fewer than five leading figures -- three dancers and two skaters -- have come over in the last month. They come despite the most rigid screening and controls, and even though relatives are commonly held at home as hostages against their return, and though political capital, in which they have no particular interest, is often made of their defection. Now, in all but open acknowledgment that the tide -- and the embarrassment -- can be stemmed only in such a crude way, Soviet authorities have cancelled the American tour of the Moscow Symphony Orchestra. The cancellation is an advertisement of official despair.

It does no good to romanticize the reasons behind the defections. No doubt some of the defectors come simply to acquire more of the perquisites for which their success in the Soviet Union has given them the taste, and some may arrive as a consequence of the personal rivalries and ambitions common to artists of all countries. Yet there can be no doubting the fundamental motivation: artists ask more from their societies than ordinary people, and in the Soviet Union artists are denied the opportunity for creative exploration and expression that they need as others need water and air. No level of favor and privilege can ultimately compensate. The defections are not merely a comment on the defectors but on the society they leave behind.

The Moscow orchestra had wanted a guarantee that any musician defecting on the planned American tour would be shipped back home. It was a characteristic demand, and an arrogant one, and one that Americans devoted to the principle of individual choice could not grant. So the orchestra will not come. Other restrictions may yet be put in the Soviet-American cultural exchange program. This is regrettable but not disastrous. It is pleasant to have Soviet dancers and musicians perform in this country, but it would be intolerable to find the United States doing the work of the KGB, the Soviet police. Few people could have anticipated that the most meaningful aspect of cultural exchange would involve the exchange of Soviet restrictions for American liberties by the Soviet elite, but the United States is the richer for it.