None of the members of the contra guerrilla group that killed American volunteer Benjamin Linder during an attack in Nicaragua last April 28 were asked to detail the exact circumstances under which he died, according to a CIA report released by a congressman yesterday.

The leftist Sandinista government maintains that an unarmed Linder, 27, of Portland, Ore., was shot in cold blood. The U.S.-backed contras maintain that Linder was armed and killed during a battle.

Rep. Les AuCoin (D-Ore.), in a letter to Secretary of State George P. Shultz, noted that none of the CIA questioners had asked the contras if Linder was shot in the heat of battle or later at close range. "I find all of this incredible," he wrote.

AuCoin described the State Department's investigation into the circumstances surrounding Linder's death as "halfhearted."

The CIA document was declassified at AuCoin's request.

The CIA report released by AuCoin is a four-page investigation summarizing the result of interviews with the contras involved in the assault. According to the report, a dozen contras were involved in what they believed was an attack on 10 Sandinista soldiers.

AuCoin released reports from pathologists in Wayne County, Mich., and San Antonio, Tex. Both support the contention that Linder may have been shot at close range.