Reports that Soviet troops have used chemical weapons against resistance forces in Afghanistan began trickling into Pakistan not long after Moscow invaded Afghanistan in 1979. Shortly after taking office, the Reagan administration pounced on these reports and in the course of the past year has built a major propaganda offensive around them.

Last March, Deputy Secretary of State Walter J. Stoessel Jr. charged in Senate testimony that 3,042 Afghans had died as a result of chemical attacks launched by Soviet or Afghan troops. When questions were asked abut the validity of Stoessel's evidence, State Department officials countered that the standards for evaluating the poison gas reports were extremely strict and that, in all probability, the death toll was far higher than the administration figure. As proof, they issued a 31-page report documenting evidence of Soviet or Soviet-inspired chemical attacks in Afghanistan and in Southeast Asia.

But to many people who are familiar with the war and the Afghans involved in it, the evidence is far from conclusive.

It contains no medical confirmation of symptons, no laboratory tests confirming the presence of toxic chemicals, no captured Soviet hardware. Most of the evidence appears to have come from personal testimony of alleged victims and witnesses to reported attacks or from Afghan army defectors. No other Western country has come up with substantive supporting accounts, nor have any of the numerous independent relief agencies working with Afghan refugees, or other knowledgeable observers.

Even America's friends here have begun to wonder whether the Reagan administration's high profile and strident rhetoric on the subject have not become counterproductive.

For instead of nailing the Soviets by concentrating on the many visible and readily accessible examples of human suffering in Afghanistan, Washington has has maneuvered itself onto the defensive in a propaganda war it should be winning hands down. Further, any clouds of doubt or suspicion cast over such widely publicized charges have a tendency to extend to other U.S. statements on Afghanistan, diminishing their impact.

Certainly the accounts provided by many refugees and Afghan army defectors have been compelling. Indeed, they have convinced many thoughtful, respected U.S. officials that the Soviets have employed toxic chemicals.

"I just can't believe that people with no real knowledge of such things could match the description of certain chemical agents so accurately," said an American embassy staffer here who has dealt with refugees.

But U.S. Embassy officials in Pakistan and India who are closest to the scene and have had most of the initial contact with refugees, admit that they have found no "smoking gun."

Ironically, one problem in finding it is that neither resistance leaders nor many of the Afghan doctors treating the sick and wounded in Peshawar share the administration's zeal for pinning down the presence of chemicals.

In a conflict so brutal, with devastation so widespread that 20 percent of Afghanistan's population has fled its terrors, some Afghans are genuinely puzzled over the dogged U.S. quest for something responsible for only a small fraction of the country's collective agony.

"How does poison gas differ from killing someone by hacking his nose and ears off and letting him bleed to death?" a resistance leader said with a shrug.

Some Afghans in Peshawar have become annoyed at the U.S. persistence in connection with the chemical warfare issue.

"Isn't this enough?" said a young physician, Tajuddin Milatmal, surveying his patients at a convalescent hospital. All the young men were minus at least one limb.

In the village of Kerala, in the northern Kunar Valley, Afghan army troops three years ago executed every male they could find after fighting around the village.

More recently, the bombardment of Kandahar, the country's second largest city, was so devastating that it shocked even senior Marxist party officials who visited the scene.

The carnage of Kerala and Kandahar have at least one common element. All were well-documented examples of human suffering in a war conspicious for the level of its cruelty.

So far, the U.S. charges of chemical warfare lack this crucial element. Without it, the charges threaten to weaken rather than strengthen the Afghan resistance cause.