A U.S. Army officer bled to death three years ago while in Soviet custody in East Germany because his captors denied him medical attention when he refused to sign a confession absolving the sentry who shot him, U.S. intelligence sources say.

"They basically tortured him," a Pentagon intelligence source said of the Soviets' conduct in the hours before Maj. Arthur Nicholson died of a wound to the abdomen.The sources said Soviet medical personnel were placed in full view of the dying officer and the Soviets promised he could have medical aid on condition he sign the document saying he had trespassed in a restricted area.

Pentagon spokesmen have disclosed that the Soviets apologized for the incident during recent Moscow summit talks between Defense Secretary Frank Carlucci and Soviet Defense Minister Dmitri Yazov.

U.S. officials had pressed for a formal apology for three years because of what one intelligence source termed "extraordinary brutality."

Army Brig. Gen. Roland Lajoie, Nicholson's commanding officer, said of the apology, "It was a long time coming, but the Soviet military has made the right decision. I am personally very pleased."

U.S. intelligence sources, providing the most complete account of Nicholson's death to date, said he was shot while taking part in a U.S. military liaison mission assigned to reconnoiter sensitive Soviet and Warsaw Pact military facilities in East Germany.

According to sources, Nicholson and his driver, Jesse Schatz, had driven to Ludwiglust, East Germany, on March 24, 1985, to try to discover and photograph new compositive and reactive armor installed on Soviet tanks.

Under post-war agreements, Soviet and U.S. forces are allowed to mount "observer missions" into each other's territory to collect intelligence, Pentagon officials said.

"The scoop is that Nicholson was inside a Soviet tank shed when a sentry shot him," a U.S. intelligence source said.

Pentagon officials confirmed that Nicholson said, "Jesse, I'm shot," after one of three shots from a Soviet sentry ripped into his abdomen.

A Pentagon spokesman quoted Schatz as saying in his deposition that the Soviets "left (icholson) where he fell for six hours."

What incensed Pentagon officials was that Nicholson could have been saved, sources said.