Contra forces have executed prisoners, forcibly recruited soldiers and killed civilians, according to the first report of a human-rights association that Congress mandated as a condition of U.S. aid.

The report covers a dozen incidents, including the deaths of eight Sandinista prisoners and eight civilians, the forced recruitment of four Mennonites, and the recruitment of 53 people by a since-arrested commander who the association said conscripted Nicaraguan Indians through "psychological pressure."

The Nicaraguan Association for Human Rights, funded by $3 million from the $100 million U.S. aid package, was set up last fall. It has encountered friction with rebel commanders.

In all, investigators have concluded or are looking at 22 "major cases of alleged human-rights abuse," the report said.

Among the cases investigated was the April death of U.S. citizen Benjamin Linder, who worked on hydroelectric projects in Nicaragua.

The report concluded he was killed in an ambush by contras who had heard that a Sandinista patrol with a Cuban and another foreigner was in the area. There was conflicting testimony from participants as to whether Linder fired a weapon in the battle, it said.

Because the Nicaraguan government refused to cooperate, the investigators could not corroborate a government coroner's report that Linder was shot point-blank.

The group said it referred allegations of human-rights abuse by Nicaragua's ruling Sandinistas to organizations such as the Organization of American States because its assignment is to monitor the contras, not the Sandinistas.

Contra spokesman Bosco Matamoros disputed the report's comment that some contra leaders view the human-rights investigation "as little more than a public-relations effort."

The report cited "reluctance" by some contra commanders to cooperate with the investigators. But Jose Tijerino, the Washington spokesman for the human-rights group, said contra commander in chief Enrique Bermudez has been highly cooperative, and better relations with the association are already apparent.

Among the cases cited in the report were:

The Aug. 2, 1985, capture by contra forces of the village and military garrison of Cuapa, in which 12 Sandinista prisoners were taken, four of whom decided to join the contras. The other eight were executed nearby by order of a commander called Atila. An earlier contra human-rights panel said only that four people were killed in fighting or while trying to escape.

The March 1986 capture of eight Nicaraguan Mennonites from the Honduran border area of Moriah, in which the contras "acted to intimidate and forcibly recruit" them. Four older men were released, two may have escaped and Bermudez assured the association in writing on April 22 that the others could be interviewed and leave if they wish.

The killing of three Nicaraguan Baptist relief workers and a Catholic Church social worker by a patrol of contra "couriers" in July 1986. The Baptists' house and the San Jose de las Mulas clinic where they worked were burned. A "policy of abducting civilians" practiced by Ampinio Palacios, known as Commandante M17, who has since been arrested by Honduran authorities. The report said he took 18 Sumo Indians in May 1986 from a refugee settlement, and in March 1987 reportedly took another 35 from Nicaragua.

Three Sumos were said to have been executed when they refused to go on a forced 23-day march. Those interviewed, some under age 16, said they had not been kidnaped, the report said, but "it was evident the majority had been taken under psychological pressure."