The freeing of Anatoly Scharansky is the stuff of an epic. For trying to hold his government to its Helsinki human rights pledges -- in the Soviet Union this is "dissidence" -- and for being presumptuous enough to seek emigration as a Jew, he was mercilessly persecuted for a decade and more. The unceasing labors of his wife, who was abroad, helped make his name an internationally known symbol of struggle against tyranny. He became one of the famous human rights "cases." Yesterday, the Kremlin released him to soften its image in the West a bit. Although he was not a spy, he was made part of a package in which the other prisoners freed by both sides were spies. He went at once to Israel.

When someone unjustly imprisoned is freed, it is an occasion for rejoicing. A shadow, however, hangs over the day. Moscow's decision to release Mr. Scharansky indicates a political decision, and is welcome on those grounds. Mikhail Gorbachev deserves no praise, however, for ending a cruelty the Soviet Union should never have inflicted in the first place. The truer measure of Mr. Gorbachev's policy is his insistence that one other similarly well-known Soviet dissident, Andrei Sakharov, will not be freed. An excuse is offered: that the one-time developer of the Soviet nuclear bomb still knows too many secrets. The likelier truth is that the moment is not yet right.

Like its predecessors, the Reagan administration enters nervously into these bizarre transactions. It wants the many benefits of rescuing human lives, but fears becoming vulnerable to sentimental blackmail. So it tries to convey to Moscow that its principles and its public alike compel it to demand at least a minimal Soviet showing of respect for human rights and for Soviet promises to respect them. It does so knowing that the Soviet system denies the Western concept of human rights and that the Kremlin, in seeming sometimes to respect the concept, is merely putting on a show. The show, however, helps a few brave people.

The West has experimented with a range of theories and tactics to induce the Soviet Union to loosen up. There is an argument for "quiet diplomacy" and an argument for public pressure. What emerges from the record is an awareness that in Moscow all human rights decisions are state decisions. First, the Kremlin wants control of its subjects, by whatever means. Second, it wants profit or the cutting of losses abroad. In times such as these, when the Soviet government is looking for something in the West, it makes the sort of gesture the world saw yesterday at the Glienicke Bridge.