Mikhail Gorbachev's statement, candid by Soviet standards, still leaves us in the dark about the cause of the Chernobyl accident. His reference to a "sudden power surge" as the starting point suggests the trouble began with an uncontrolled chain reaction rather than with a failure of the cooling system, as postulated up to now by Western analysts. What caused the power surge, how it was related to the refueling going on at the time, and whether this was somehow related to plutonium production remains a mystery. The Soviets must have a good idea of what happened; they recovered the control room records and undoubtedly interrogated the operators. But they aren't saying.

The Soviets haven't told us much about the radiation impacts, either. They gave the International Atomic Energy Agency a few scraps of information that it had no way of checking. We will probably never know with any certainty the radiation impact on the nearby population, especially after their evacuation and dispersal. More important, the Soviet public will not know.

The failure of the Soviets to inform the rest of the world promptly pales beside their slowness to move their own people out of harm's way. We need to remember that the health effect outside the Soviet Union was slight; the brunt of the disaster fell on the workers at the site and on the surrounding population. The evidence points not so much to Soviet malevolence as to ineptitude born of secrecy and bureaucratic rigidity.

For the first couple of days, the Kremlin probably could not figure out what was going on. Very likely, frightened officials at the site underplayed the accident, hoping to bring it under control before their bosses got the full story. Delaying evacuation would fit with this outlook. (The response at Three Mile Island was not so very different, though happily the result was.)

One thing the Soviets will not be able to hide is whether the evacuees are allowed to return and whether any land remains unusable after several months. The dangers of iodine-131, which accounted for a large part of the radioactivity released, are cut in half every eight days, and so are negligible after several months. By contrast, cesium-137, another isotope released during the accident, remains radioactive for decades. It does not take much of it to put many square miles off limits for permanent residence -- barring a cleanup of unprecedented proportions.

In view of our present ignorance, it is too early to decide what the lessons are for us. For example, it isn't yet clear whether Chernobyl had some sort of containment structure around the reactor, or whether our containments would have withstood the force of the Chernobyl explosion. While our containments are likely to be very valuable in a wide range of accidents, they are not designed to cope with the most serious kinds of accidents (those involving melted uranium fuel), and the Nuclear Regulatory Commission licensing review stops short of considering such accidents. Reexamining this line of defense, at least for reactors in regions of high population density, would be a useful response to the Soviet accident.

Altogether, one would feel more comfortable if the instinctive response from nuclear industry and government placed less emphasis on calming the public and more on going back and checking out our own systems. If we could only explain to these nuclear officials that we are not going to panic in the meantime. Would they please just carry out their own responsibilities? There will be plenty of time to make comparisons between U.S. and Soviet nuclear safety when we learn more about the accident.

In order to learn more, we are going to have to deal with the Soviets more closely than before on nuclear safety. Let us hope that the effect will be to open up their system. But secrecy is insidious. For example, in order to get information on current radiation levels from the Soviets for regulatory agencies in various countries, the IAEA has apparently agreed that the information will not be made public. The one thing we don't want to do is to adopt Soviet habits.