Beyond the immediate horror, what's especially sinister about the repeated though sketchy reports of Soviet gas warfare in Afghanistan is that if they are true, nothing can now be considered out of bounds in the arsenals of East and West.

And what this means is that the fertile minds that serve the financially lush military laboratories of the major powers may now be closer to that go-for-broke working regime that the hard-liners have persistently sought. The possibilities are endless, ranging from such well-publicized fields of military inquiry as biological warfare to the murky and little-talked-of interest in what's known as environmental warfare -- turning the weather and other forces of nature against an opponent. That biological and environmental warfare are restricted by international agreements is not especially reassuring. Gas warfare is also restricted, but a large accumulation of evidence -- apart from whatever is happening in Afghanistan -- indicates that the Soviets are heavily prepared to use it offensively, while the U.S. Army is seeking a rapid buildup of its chemical forces.

Though the military value of gas warfare is open to serious question, gas has long been the symbol of a self-induced weapons abstinence that constitutes an acknowledgment that some things are just too awful, even in all-out war. As a result of the devastation produced by its surprise debut in World War I, gas warfare has been uniquely fettered by a universal sense of revulsion coupled with fear of reprisal in kind.

Opponents of gas have correctly emphasized that it is a difficult-to-manage and unpredictable weapon. But even in cases where it would have been simple to manage and highly predictable -- such as against Japan's fortified island outposts in World War II -- the psychological restraint prevailed against military advantage. In the long history of organized killing, this is, of course, an oddity, since other means of inducing swift or agonizing death are accepted with few quibbles. But for whatever peculiar reasons -- including, it seems certain, a sense that it's reprehensible to attach death to the necessity of breathing -- gas warfare has been deemed so "unclean" that not even Hitler employed it. In Vietnam, the United States used gases for military purposes, but always insisted that these were non-lethal gases designed to force people from hiding so that they could be attended to with socially acceptable weapons.

In any case, though improvements have been made in miltary gases, their delivery and the means of shielding their users against the effects of perverse winds, the stuff is still regarded as so loathsome that 115 countries, including all the major powers, are parties to the prohibitions written into the Geneva Protocol of 1925. This agreement, however, has not prevented research, production, stockpiling and training for chemical warfare; nor, if the Afghanistan reports are correct, has it inhibited the Soviets from doing as they please, though there is the minuscule loophole of Afghanistan's not being a party to the protocol.

If the barrier is down on gas warfare, the prospects for maintaining inhibitions against other estoric means of killing are inevitably lessened. Though environmental warfare is prohibited by the 1977 convention on "Hostile Use of Environmental Modification Techniques," it nonetheless possesses an alluring economic and military potential in a resource-short world. Slight changes in average rainfall or temperature can have profound effects on agricultural output -- which is the main use seen for environmental warfare. But there are other possibilities, as indicated by reports -- repeatedly denied -- that the United States tried to wash out the Ho Chi Minh Trail with man-made rains. Given the claimed proficiency of the rain-making craft, it is difficult to believe that the military didn't at least look into the matter very seriously. And then, too, not to be left out of the environmental weapons catalog are such sources of disaster as earthquakes and tidal waves. It sounds too bizarre to be credible and, it must be noted, U.S. defense-research managers insist they are not pursuing this stuff. But in terms of the basic scientific understandings that would have to underpin environmental warfare, they don't have to pursue it. For purely benign purposes, weather modification, earthquakes and tidal waves are the objects of extensive civilian-run research.

If the Soviets have, in fact, rid themselves of restraints against gas warfare, the psychological effects on American military and political thinking will be far greater than any potential battlefield effect. Troops can be protected against gas, and chemicals can be met with chemicals. But in the process, East and West will have lost the irrational, fragile, but hopeful idea that some weapons are too horrible to be used.