ANOTHER WISP of information about the Sakharovs came out of the Soviet Union the other day. It was a postcard sent to her American children by Yelena Bonner, Andrei Sakharov's wife, who was reported in August to have been sentenced to a five-year term of internal exile in Gorki for anti-Soviet conduct. The children described the postcard as the first authentic message received from Miss Bonner in the West since April. It was, however, far from a complete and satisfying message. Internal evidence indicated it was probably wrongly dated. There was no mention of Andrei Sakharov or of Miss Bonner's health, and no indication of whether the two are together.

In brief, the postcard is one more piece of evidence of the KGB at work. Its commissions and omissions suggest that the hand on the pen writing it was not Miss Bonner's alone. The postcard is the latest in a series of official releases of different sorts indicating that Moscow hopes to reduce the Sakharov question as an irritant in Soviet-American affairs. All these releases, however, raise questions of their own. They are tantalizing yet, finally, insubstantial. Their deadly aura of official manipulation deprives them of credibility. The very Soviet effort to quiet the issue down furnishes disquieting new evidence of the arbitrariness of Soviet power.

All these wisps of official information, part-information, mis-information and perhaps dis-information, when added up, do not provide the truth that would come from one firsthand report by a reliable independent witness. That is one of the abiding lessons of the Sakharov affair, and its implications are bound to fall across a range of other Soviet-American concerns. If, as many Americans hope, the Kremlin is considering whether to cross a threshold into a stage of improved relations with the other superpower, then it has powerful reason to clear up the doubts still hanging over the fate of the Sakharovs.