Amid charges and countercharges about the use of chemical warfare in Afghanistan, new evidence points an accusing finger at Moscow.
On the one hand, the Soviets accuse the anti-government guerrillas of using chemical weapons supplied by the United States and Britain. No evidence has been offered to support the claim.
On the other hand, the West (especially Washington) vigorously contends that Moscow and its Afghan client have frequently employed such lethal agents in their efforts to crush the guerrilla resistance.
Now, another Soviet soldier captured by Afghan guerrillas has said that occupying Soviet troops have used lethal chemical agents. According to his account, tape-recorded by guerrillas and supplied to reporters, two types of chemicals caused a dense yellow cloud and were about 30 percent lethal. A third agent was 100 percent lethal.
The soldier's testimony provides additional but extremely valuable oral evidence in the alleged use of chemical warfare by Moscow. Other Soviets captured by the guerrillas have referred to the presence of chemical and biological agents in Afghanistan. This soldier claims to have been taught chemical warfare in Kabul. He also says a Soviet helicopter pilot once ordered him to don a gas mask during an attack on a guerrilla camp.
At least one Russian prisoner and several Afghan Army defectors interviewed by Western journalists have maintained they were deployed in areas where chemicals were sprayed. As in Vietnam using defoliants against crops has become normal procedure in Russian attacks. Categorized by the Soviets themselves as ''weapons of mass destruction,'' chemical and biological agents were reportedly stocked in Afghanistan shortly after the December 1979 invasion.
In theory every soldier in the Red Army is said to be equipped with a respirator and chemical protection suit, but whether such protective equipment has been systematically issued in Afghanistan remains unclear.
Both Western and neutral analysts still lack the necessary tangible proof to put the clincher on the chemical warfare controversy, namely a canister bomb or aerial spray tank used for such purposes.
But increasing circumstantial evidence ranging from refugee reports to medical testimony makes it virtually certain that the Soviets have made widespread use of lethal nerve gases and toxins as well as nonlethal incapacitating agents normally used for riot control.
During assignments to Pakistan and Afghanistan over the past 2 1/2 years this correspondent spoke to a number of resistance fighters and refugees claiming similar conditions. Even skeptics regard these accounts as compelling. It is difficult to believe that simple, nonliterate tribesmen could have any real prior knowledge matching the description of certain chemical agents so accurately.
Earlier this year the US State Department maintained that more than 3,000 Afghans had suffered from chemical warfare attacks. The Kremlin has repeatedly rejected such accusations as ''absurd.''
Neverthless the Soviet Union tried to prevent the dispatch of a three-man team to Pakistan by the UN General Assembly in February of this year to report on the situation. Unable to enter Afghanistan itself, they visited refugee camps to interview eyewitnesses and surviving victims.
Their 36-page report, which is to be officially released at the next General Assembly this autumn but has already been leaked to the public by the Wall Street Journal, confirmed US allegations.