It was a day of agonizing uncertainty for the friends and relatives of the American hostages aboard the luxury liner Achille Lauro, a tempestuous day that ended with relief and deliverance -- except for the family of Leon Klinghoffer.

Klinghoffer, a crippled, 69-year-old retired owner of a Manhattan appliance shop who was seeking rest and camaraderie on an autumn cruise through the Mediterranean, was mysteriously singled out from among more than 400 hostages and killed by Palestinian terrorists.

Reports last night that Klinghoffer's body was dumped over the side of the Italian ship on Monday ended a day that had begun with a tragic fragment of misinformation -- that the terrorists had surrendered with all hostages safe. "Let the party begin," a jubilant Lisa Arbittier, Klinghoffer's daughter, told reporters yesterday morning.

That brief exuberance turned to despair, then to grief last night when, after hours of uncertainty, Klinghoffer's murder was confirmed in a call from the State Department. Letty Simon, a close friend of the Klinghoffer family, left the Klinghoffers' Manhattan apartment and told reporters, "We have confirmation from the State Department that he is dead. The family will not come down this evening. It is personally a very difficult time for them."

Perhaps foremost among the many mysteries around the two-day piracy ordeal is why Klinghoffer, paralyzed on the right side after a stroke five years ago that left him with slurred speech, was singled out by the four Palestinian hijackers.

The dead man was one of a group of 11 friends and relatives from New York and New Jersey, mostly frail retirees, who had booked the $1,700, 16-day cruise on the Achille Lauro.

News of Klinghoffer's death was first reported by the Italian Prime Minister Benito Craxi at a news conference in Rome around midday Eastern Daylight Time. But throughout the day, there were conflicting reports of violence aboard the cruise ship. Klinghoffer's 58-year-old wife, Marilyn, was apparently unharmed.

Before final confirmation of the death was received, family friend Carol Hodes offered a poignant portrait of Klinghoffer: "I've known him for several years. He doesn't hear well. He's got slurred speech, and he spends a lot of his time in a wheelchair. He's hardly a threat to anybody, and I can't imagine why anybody would want to hurt him."

Neighbor Judy Tomasho added, weeping, "Even after his stroke, he would be out here every morning in his wheelchair, greeting people, asking after their children, just being a nice guy."

The grief for Klinghoffer contrasted with relief and joy elsewhere around the country -- in Chicago; Fort Lauderdale, Fla., and the small town of Lincroft, N.J. -- where families of the released hostages heard television news reports.

Throughout the two days, most families kept in touch with developments through a phone line to the State Department and the re- porters camped in their living rooms.

"I am here with 25 newsmen and my dog," said Hodes, whose mother, Mildred, 64, was aboard the Achille Lauro, while her father, Frank, 66, unwittingly avoided the hijacking by taking a 15-hour bus tour of Cairo and the Pyra- mids.

Phyllis Yellin, 44, whose mother, Sophie Chasser, 69, was one of the hostages said: "I have mixed emotions. I am happy that Mom is alive, but I would not mind meeting the hijackers on a dark night with a machine gun."

Yellin added that she was alarmed by the apparent inability of the United States to counteract terrorism. "We ought to be carrying a big stick, but in fact we are just carrying a twig. We have got missiles and satellites, but nobody seems to be able to do anything."