The body of Peter Kilburn, an American librarian killed in Lebanon last week in apparent retaliation for the U.S. bombing raid on Libya, bore no signs of torture or other mistreatment, Kilburn's nephew said yesterday.

Timothy Kilburn said in a telephone interview from his home in California that his uncle's body had undergone an autopsy at Bethesda Naval Hospital before being flown to San Francisco yesterday for burial next week.

The nephew said State Department officials told him that Kilburn, 61, had died from a single bullet wound in the back of the head.

Otherwise, he "was in fairly good shape, clean, with a few days' growth of beard. He had lost a lot of weight" during his 16 months as a hostage, Timothy Kilburn said, "but we knew that already. There were no signs of torture."

Peter Kilburn was kidnaped Dec. 3, 1984, in Moslem West Beirut. He and two British teachers abducted about a month ago were found shot to death April 17 near a mountain lane east of Beirut.

A group calling itself the Arab (Fedayeen) Commander Cells said that it had killed the three men in retaliation for the U.S. attack on Libya April 15.

The nephew said that he had resisted the idea of an autopsy "because I thought it was unnecessary" in positively identifying his uncle, but offered to allow it to ensure that the family would not be asked to pay the cost of flying Kilburn's body from Washington to California.

John Adams, the State Department official who handled the arrangements, said there never was any intent to ask the family for payment, and that there was no linkage to Timothy Kilburn's permission for an autopsy.

Timothy Kilburn said no one had told him officially that the family might have to pay, and American University in Beirut, where Kilburn had been chief librarian, paid for that flight.

At least four American hostages still are held in Lebanon.