Allegations by the US government that the Soviet Union is using chemical weapons in Afghanistan are based on essentially circumstantial evidence. But what is deeply disturbing is the fact that the shreds of evidence -- information supplied from Afghan army defectors, refugees now living in Pakistan, and analysis of recorded military operations -- now seem to be taking a coherent shape in a particularly unpleasant mosaic. For if it turns out to be true that the Soviets are using poison gas and other lethal chemical agents, they may be doing so in violation of the Geneva Protocol of 1925, which bans the use of such weapons. The allegations should be given careful examination by the world community, and in particular, the United Nations.
The latest US claims regarding Afghanistan come from a highly respected foreign service official, Deputy Secretary of State Walter Stoessel Jr. In testimony before Congress Mr. Stoessel charged that such attacks in Afghanistan ''have been conducted with irritants, incapacitants, nerve agents, phosgene oxime and perhaps mycotoxins, mustard, lewisite and toxic smoke.''
According to the State Department, Soviet forces have killed as many as 3,000 people in Afghanistan by using poison gas and other chemical weapons. Such allegations have been made by the US several times since the Soviets first invaded that country back in December 1979. But until now the US has refrained from releasing much detail to back up its claims. The Soviets, meanwhile, have repeatedly denied using such weapons.
One issue that would likely have to be addressed is whether any Soviet use of chemical agents in Afghanistan -- assuming such agents have been used -- should be considered an ''internal'' affair or ''international,'' since the prohibitions of the Geneva Protocol have sometimes been interpreted as meaning no use by one national state against another national state.
It would also be important that a clear distinction be made between use of lethal and nonlethal gases, such as tear gas.
The world community would surely want to know the truth about such representations. The issue transcends the usual broadsides and counterclaims flying back and forth between the two major world superpowers. World public opinion has rightly looked upon the use of poison gas as especially reprehensible, growing out of the terrible experiences in the trenches of WW I. The question must be raised that if a nation were in fact willing to use such a dreadful weapon in contravention of an existing international treaty and/or the clear opprobrium of world opinion, might it not be equally willing to violate other international arms control agreements?
For these reasons, the poison gas allegations demand the close attention of all nations.