QUITE SUDDENLY the possibility arises of Soviet and American agreement on banning chemical weapons -- production, storage, transfer, use. These are not the main weapons in either great power's arsenal, but they have a special aura of horror and are part of the immense attack capability the Kremlin has prepared in Europe. Since chemical weapons are available to nonnuclear countries as well as to nuclear ones, the international negotiations organized to contain them have gone on in the 40-nation Committee of Disarmament in Geneva. For years Moscow stonewalled and no progress was made, but now Soviet policy has changed, possibly in part because the Reagan administration finally persuaded Congress to start down the road to producing new chemical weapons -- a development we thought was wrong and still think is dangerous, but which seems to have had a useful strategic effect.

According to the Kremlin, the Soviet Union has already stopped producing chemical weapons, does not store them outside its borders and will destroy its stockpiles upon conclusion of an international treaty. Demonstrating the new Soviet embrace of on-site inspection, foreign experts, including American officials, were recently invited to the Shikhany chemical weapons facility. But the visit, presumably intended to build confidence, built doubt too. Not all the weapons the Soviets are thought to possess were put on view, and the Kremlin still insists it will not report on its stockpiles until a treaty is done.

Chemical weapons are easy to make, in factories that can be quickly converted from civilian usage, and easy to hide. On-site inspection is useful but, especially in this area of arms control, no panacea. A verification scheme may be possible that reduces chances that cheating will go undetected and increases the political costs to the cheater. These are minimal standards, however, and a treaty meeting them might not survive the intense scrutiny it would surely get and deserve in American political debate.

It makes sense to think of chemical weapons limitations in the context of a larger agreement on dismantling the Kremlin's whole European invasion capability, of which chemicals are just one part. Meanwhile, Moscow is welcome to show in any way it can think of that it is going out of the business of chemical warfare. And Washington should make sure its own run-up to production of a new nerve gas does not put it more deeply in.