APTOS, Calif. (AP) _ Family members of an American hostage slain in Lebanon apparently in retaliation for the U.S. bombing of Libya say they expect to see more people killed and would like to see a day of prayer to end the violence.

The body of Peter Kilburn, 62, was discovered along with those of two Britons in Lebanon's central mountains Thursday, along with a note saying they had been executed by a group called the Arab Revolutionary Cells to avenge the attack against Libya earlier last week.

''Peter was very peaceful. He loved the Lebanese people. That's the ironic part,'' Jeanne Repetto, his sister-in-law, said in an interview on Sunday.

''I don't think Peter will be the only one that will be sacrificed. I think the attack has compromised lots of Americans in Europe,'' said Mrs. Repetto, 56, of San Jose, Calif. ''There will probably be many more senseless deaths.''

She criticized the U.S. air raid on Libya, comparing it to throwing a bomb out the window to try to kill a pest.

''By throwing the bomb out the window, we've blown out the window, breaking whatever protection we had, and now we have found that, instead, we hit a hornet's nest. I shudder to think about what will happen,'' Mrs. Repetto said.

''We have to band together in international prayer to stop the violence that is killing innocent people,'' she said.

She and other relatives gathered here on Sunday at the home of Tim Kilburn, a nephew.

A statement issued by family members on Sunday asked Americans to ''build strength within ourselves to resist the temptation of violence, hatred and revenge.''

Kilburn's body was flown from a U.S. air base in West Germany to Andrews Air Force Base outside Washington on Sunday and positively identified, said State Department spokesman Bruce Ammerman. The body was to arrive in California on Tuesday, with a funeral tentatively scheduled April 30, the relatives said.

Kilburn, of San Francisco, was a librarian at the American University of Beirut for 20 years until he disappeared on Dec. 3, 1984.

He had not been seen in public since his disapparance, although Tim Kilburn said the amily had heard from unidentified sources that he was still alive until this week.

''We're angry that the United States didn't do anything to try to negotiate with the Lebanese people for his release,'' said Mrs. Repetto. ''We were told one thing one day and other things on other days, and then it seemed he was just forgotten.''

The State Department had no comment on the family's remarks, Ammerman said.

Five other American kidnap victims are still missing in Lebanon, and 51 foreigners, most of them Westerners, have disappeared in Lebanon since January 1984. Twenty-seven have been freed, and six have been found dead.

A former American hostage in Lebanon, the Rev. Benjamin Weir of Berkeley, Calif., said on Sunday that he feared for the lives of the five Americans still captive.

''The American strike against Libya has greatly increased the threat to the lives of the American hostages now held in Lebanon,'' Weir said in an interview with KPIX-TV ofan Francisco. Weir, 62, who was freed Sept. 14, grew up with Kilburn in Berkeley.

Mrs. Repetto said Kilburn had been ''suffering day by day. I feel relieved that he is out of that now. He's at peace.''