Today Andrei D. Sakharov is 65 years old. It would be nice to say "Happy Birthday," but that traditional salutation seems particularly out of place given Sakharov's current, tragic situation.

The fact that Sakharov remains a prisoner in the city of Gorki after six years of inhuman abuse, including physical torture, is a reminder that modern civilization has not ended man's brutality to man -- far from it. Of course there are countless other such reminders; they appear in this newspaper every day. The case of Sakharov is especially poignant for me because I knew him personally for nearly three years in Moscow.

Personal acquaintance with Sakharov is not like the conventional human relationship. Sakharov makes an extraordinary impression on everyone who is lucky enough to know him. Anatoly Shcharansky, for example, said in Washington last week that Sakharov is perhaps the greatest man he has ever known. I would say the same.

It is the saintliness of the man that leaves the strongest impression. Oh, yes, he is brilliant, truly a unique intellect in the world of theoretical physics and cosmology. And he is brave, willing to fight alone against the full powers of the Soviet state. And selfless -- willing to abandon his scientific career to carry on a doomed struggle for human rights in the Soviet Union. But it is the gentle saintliness one remembers -- the quiet determination, the impeccable manners.

The official treatment of Sakharov amounts to a textbook on how the Soviet system works. To begin with, it is extralegal: XR Sakharov is held under what amounts to house arrest in Gorki, surrounded by secret police, forbidden to talk to any ordinary citizen, deprived by a special jamming device even of the opportunity to hear radio broadcasts from the outside world, but never formally charged or convicted under any Soviet law. After the invasion of Afghanistan, when the Soviet leaders obviously felt they had nothing to lose by the act, they simply picked up Sakharov and sent him to Gorki.

Many Soviet officials, I am convinced, believe that this treatment of Sakharov is actually humane and generous. By their lights, he had earned much worse by his relentless provocations -- his use of his prominence to attack the Soviet system, his open courtship of the hostile Western news media, his status as the embodiment of domestic opposition to the regime. By traditional Soviet standards such a person should be in prison or labor camp, or dead.

But Sakharov himself, characteristically, has told us, in letters that miraculously reached the West, about the true circumstances of his life in Gorki. In fact he has been denied most opportunities to pursue his scientific work. His personal papers have repeatedly been stolen from him by the KGB agents who constantly surround him -- once after he had been drugged. In despair, he has gone on hunger strikes to win concessions for members of his family, most recently to try to persuade the authorities to allow his wife, Yelena Bonner, to travel to the West for medical treatment. (She is returning to the Soviet Union later this month after heart-bypass and other surgery in this country.)

In response to a hunger strike in May 1984, Sakharov was tortured. "Orderlies would throw me onto the bed, tie my hands and feet and then hold my shoulders down while the needle was inserted into a vein . . . Sometimes my jaws were pried open by a lever . . ."

Official treatment of Sakharov is also revealing about Soviet psychology. The Western world was appalled to discover, after the nuclear accident at Chernobyl, that the Soviets initially seemed more concerned about covering up a disaster than about dealing with it, or warning neighbors of its possible consequences.

That same instinct to flee from embarrassment is evident in the case of Sakharov. His dissidence has never been accepted by officials in Moscow. They have always seemed incapable of believing that a man of such impeccable background -- the son and grandson of distinguished Russian scientists and army officers, the inventor of the Soviet hydrogen bomb who was three times named a Hero of Socialist Labor, a member of the prestigious Academy of Sciences since the unprecedented age of 32 -- could have become an outspoken critic of their regime. Many officials have chosen to blame this development on Sakharov's wife, who comes from a Jewish family, though this is preposterous to anyone who knows them both. Indeed, Sakharov was launched on his dissident career before he met Yelena Bonner.

Sakharov's friends and scientific colleagues are now pressing the Soviet authorities to allow him to move back to Moscow, where he can get better medical care and resume scientific work. That would be a nice birthday present for him.

But a bolder gesture would be a nice gift for both Sakharov and the Soviet leadership of Mikhail Gorbachev -- and at a moment when the men in the Kremlin could use some help. By allowing Sakharov to leave the Soviet Union, the Gorbachev leadership could dramatically repair the damage Chernobyl has done to the new image it was so avidly cultivating before the accident. Gorbachev wants to be seen as a new kind of Soviet leader, one who confronts problems creatively and is free from old taboos and habits. What better way to revive that public relations offensive than by letting Sakharov leave?