THE CHERNOBYL MELTDOWN affords the American public a somber glimpse into the Soviet approach to arms control. Here is a case where openness and candor were naturals: the event was bound to become known, no treaty violation or security secret was involved, and immediate full notice was imperative and would have brought great returns in health and diplomacy. Yet the Soviet Union suppressed the news altogether until foreigners queried them about the fallout. It has since supplied only the most terse and incomplete explanations, some of these so strained (they couldn't inform the Swedes because it was the weekend) as to be laughable if they were not tragic at the same time.

It is commonly said that the United States pursues arms control on the theory that it can rely on its own capacity to check compliance and to detect noncompliance, and not on "trust." It is plenty disturbing nonevernment with which Americans seek agreement cannot tell the simple truth in a timely fashion when it is obviously to its own immense advantage to do so. Perhaps this should be considered in the category of old knowledge confirmed, not new knowledge gained. It is significant all the same, and it cannot fail to affect the threshold readiness of Americans to engage in sensitive dealings with the Soviet Union.

Anyway, it is not exactly true that there is no consideration of trust or good faith at all in a properly negotiated arms control text. Nuclear circumstances are never without some degree of ambiguity. Not all contingencies can be fully anticipated. Questions of interpretation arise in the most heavily lawyered contract. In the end, the verification of arms control is not self-executing. There is at least a residual requirement for confidence. The openness of American society enforces a standard of probity -- not a perfect standard but a high one -- for which there is no match in the closed Soviet system. There it all hinges on how the authorities choose to play it.

It is Mikhail Gorbachev, supposedly a new, modern kind of Soviet leader, who has to be regarded as the man in charge of information policy. In some of his earlier approaches, he had hinted at a new standard of accountability, but in this crisis so far he has clung to the old standard of denial and secrecy. Had he deliberately set out to devise a scenario to undermine his own credibility as a suitable arms control partner, he would have proceeded exactly as he has at Chernobyl.