U.S. investigators say they have stronger evidence than ever that American soldiers missing in action - including spy pilots shot down during the Cold War - were held in the Soviet ''gulag archipelago'' of prison camps.

''We believe the sheer volume of reports suggests it may likely have happened,'' said James MacDougall, senior analyst with a U.S.-Russia Cold War Working Group on POWs and MIAs. For most of the '90s, U.S. teams have scoured Russia for information on MIAs from Korea, Vietnam, World War II, and on dozens of aviators who went missing on Cold War spy missions in the '50s and '60s. The search focuses on 10 missions and 77 missing men, centering on Russia and the former Soviet republics. U.S. investigators have interviewed pilots who gunned down U.S. aircraft, and have watched gun-camera film once shown to dictator Josef Stalin. The trail of the Americans through the Siberian taiga has run hot and cold, said MacDougall. But a ''memoir'' turned over to U.S. officials and reviewed by Gannett News Service contains new information and at least one firsthand sighting. U.S. officials won't name the author, a Russian who spent decades in Siberian ''internal exile.'' The unknown author reports seeing an emaciated American named ''Dale'' in January of 1953. The encounter occurred at a uranium mine on the island of Rybak off the Soviet Pacific coast, where Dale had been sent by Soviet jailers to make engineering repairs. Officials confirm that an aviator named Dale remains among the missing.