ALTHOUGH THE COST will have been high, perhaps the reactor disaster at Chernobyl can lead to a stronger and broader international code of nuclear safety. Two current developments offer at least qualified grounds for optimism. The seven industrial democracies at the Tokyo summit meeting called for an agreement committing governments to report nuclear accidents. The seven evidently intend to build on the voluntary guidelines adopted two years ago by the International Atomic Energy Agency. At the same time, the Soviets have invited the director of the IAEA, Hans Blix, and two of his deputies -- respectively a Russian and an American -- to Moscow to discuss the meltdown at Chernobyl. It is a signal that the Soviets do not consider the IAEA to be an adversary, and perhaps are preparing to use it as a conduit to give the rest of the world a better description of the accident.

But it's not yet time to celebrate. The communique from Tokyo speaks of a convention only on accident reporting, not on safety. Safety is a more complex subject, particularly if it is to be enforced with inspections. But the world's leading producers of nuclear power and builders of nuclear equipment -- the countries at the Tokyo meeting and the Soviets -- have a responsibility to move promptly toward a safety standard that is both binding and explicit.

Recent experience is a warning of the difficulties here. In 1981, following the accident at Three Mile Island, the United States proposed a binding convention on safety. The idea was strangled at birth. It appears that some of the responsibility lies with European countries whose nuclear industries were anxious to export reactors and who feared that tight safety standards might inhibit sales to those countries, particularly in the developing world, that would have difficulty complying. There were claims that safety standards would violate national sovereignty. But that argument has been effectively answered by the events at Chernobyl and the clouds of radioactive debris now following the wind with little deference to national boundaries.

When the American initiative failed, the IAEA cautiously moved toward the present voluntary guidelines on safety. They are less than the world now needs, but they provide a base on which to construct a stronger structure. The IAEA has always considered its chief responsibility to be its efforts to prevent the spread of nuclear weapons. But its experience with international inspections and enforcement is, for all of the limitations, a promising precedent on which to build the world's first attempt at mandatory rules for nuclear safety and environmental protection. Chernobyl, like all disasters, is a warning. How likely is it to be repeated? That depends on the skill and vigor that governments, not only in the Soviet Union, now bring to the reinforcement of the rules for nuclear safety.