THE FIRES at the Chernobyl reactor are evidently extinguished. Officials of the International Atomic Energy Agency have confirmed that report, after a helicopter flight around the site. It's probably too early to say that the damage is entirely under control, but the Soviets are working vigorously to seal the plant's radioactive core in concrete. On the basis of what's known here, it's fair to say that the Soviets' first reaction to the explosion was very slow, and the evacuation of the nearby towns should have been carried out sooner. But since then the emergency crews seem to have been working with skill and, it should be said, notable courage. To do what they have done, many people must have put their lives at great risk.

It will be some time before the full effects on human health can be fully calculated. The immediate toll, fortunately, seems clearly to have been lower than most people outside the Soviet Union initially thought possible. But the long struggle with the further effects of the radiation is only beginning. The damage to crops and the contamination of water supplies have yet to be assessed.

Out of this immensely costly catastrophe, what lessons can be gained? The world clearly needs a better system for notification of accidents. The IAEA has been trying since 1982 to develop a comprehensive worldwide reporting program. Presumably the Chernobyl explosion will help persuade the doubters. More difficult to achieve but no less necessary, the world similarly needs safety standards for power reactors -- enforced by inspections. Here again the IAEA, despite its limitations, is the most promising instrument.

Every country has its own reasons for uneasiness about international safety rules and inspections of its reactors. The United States will worry that once again it provides greater access than the Soviets do. The Soviets will, as usual, worry about military espionage -- and with reason, since some of their power reactors also produce plutonium for weapons. The developing countries will be particularly difficult to draw into the system. Many will see the safety standards as a covert attempt by the rich countries to put nuclear technology beyond their reach. It's entirely true that a lack of industrial experience makes it harder for a country to meet rigorous standards -- but that's another compelling reason to have them, since many developing countries are now building reactors. The answer to their suspicions is to point out that the two most dangerous reactor accidents of the past decade were in, respectively, the United States and the Soviet Union -- the two countries with the clearest responsibility now to advance the international enforcement of nuclear safety.