US: hard evidence of chemical weapons

The State Department says it has conclusive evidence that Communist forces are using deadly chemical weapons against tribesmen in Laos, Cambodia and possibly Afghanistan.

The government has completed an anlysis of plant and water samples from Southeast Asia that were contaminated with chemical poison.

Officials say this is the ''smoking gun'' that critics demanded when Secretary of State Alexander Haig charged in September that the Soviets and their allies were waging chemical warfare.