Mr. Sakharov, the father of the Soviet hydrogen bomb, had, from his "internal

exile" in Gorki, written a letter to an American scientist prominent in the nuclear-freeze movement in which he said, "The main danger is slipping into an all-out nuclear war. If the probability of such an outcome could be reduced at the cost of another 10 or 15 years of the arms race, then perhaps that price must be paid ..." The reaction in Moscow had been, in Mr. Buckley's description--which Mr. Bundy endorses--"near hysterical." This rich discussion, which moves from the arms race to the current state of NATO to the "exaggeration," as Mr. Bundy has it, in President Reagan's hopes for SDI, starts with the letter itself. MB: "This letter is a perfectly extraordinary example of the imaginative and intellectual force of Sakharov's mind and of his independence. As one man thinking for himself, it's, I think, one of the truly extraordinary documents of the nuclear age,... and

I think that really it is just that force, the unconquerable spirit of the man and his

independence, that is so deeply offensive to our friends in Moscow."