AT BELGRADE TODAY, the 35 countries that signed the 1975 Helsinki agreement on European security and cooperation will start reviewing how it has worked. For the United States, the question is what this review can reasonably be expected to produce. The answer starts with an understanding that the basic Helsinki principle - fresh and formal acceptance by each signatory that its internal practices are of international concern - is absolutely sound. No matter that the Russians may have signed at Helsinki cynically. No matter that no one expected the commitment would play so quickly into the next American President's particular, worldwide preoccupation with human rights. Helsinki added legitimacy and currency to any effort that free nations might undertake to lower walls between nations and to deepen concern for the way individuals are treated by the state. Helsinki also added a procedural vehicle - the review process opening today.

Early on, it seemed that Mr. Carter's approach to Soviet human-rights violations could produce a Soviet backlash damaging to other American interests. But the administration has been at pains to show that Russia is not its only target and to pursue those other interests. The Russians, though obviously irritated enough to criticize Mr. Carter rudely and personally for his policy, seem prepared to negotiate on the other matters. Belgrade may even lend itself to a further separating out of rights issues.

More troubling in another sense is Kremlin retaliation against the intended beneficiaries of American political intervention, especially would-be emigrants and dissidents. This is a real danger and one that compels tact. It compels, too, some historical pespective. Current Soviet crackdowns come against a backdrop of relative liberalization. The flow of Jewish emigrantion allowed by political tensions was itself an unprecedented flow; substantial German emigration from the Soviet bloc goes quietly on.

Individual cases are inflammatory: The phony (by Mr. Carter's say-so) treason charges brought against Anatoly Scharansky and the harrassment of American diplomats and correspondents are ugly in themselves and in their anti-Semitic overtones. Such steps constitute a gross but predictable effort to isolate Jews and dissidents, who pass to foreign cororespondents information that embarrasses the Kremlin abroad and that comes back into the Soviet Union by foreign radio broadcasts.

The Kremlin can't be expected to like this joint effort by foreigners and its own boldest citizens to expand the scant room available for individual choice or expression in Russian. Careful international pressure at Belgrade, however, can help teach the Kremlin that the effort is at least worth tolerating.

In sum, Belgrade offers a useful forum for an administration wishing to make good on its pledge to make national values an integral part of international policy. Enough experience has been accumulated, moreover, for balance to replace impulse as the basis of human-rights policy. It compromises to be a disorderly conference. The Russians will have their own complaints about American "violations" in unemployment and the like. But the process could help produce the collective pressure to accord more respect for human rights an d that is the main point.