Not long after the skies grew dark with a second day's setting sun, a Coast Guard admiral declared an end of hope tonight that John F. Kennedy Jr., his wife or her sister could be found alive in the waters that swallowed their aircraft Friday night.

"We did everything we possibly could to find survivors from this incident," Rear Adm. Richard M. Larrabee told reporters about 9:45 p.m., declaring a shift of focus from "search and rescue to search and recovery" in support of a federal investigation of the cause of the crash.

Describing a telephone conversation with the next of kin of Kennedy and of Carolyn and Lauren Bessette, Larrabee added: "It was a very difficult phone call for me, and I'm sure it was much more difficult for them. We're in the business of saving lives. . . . This is not the result we were looking for."

In a final bow to the mysteries of Providence, or perhaps only to soften the blow, Larrabee emphasized that he had not called a halt to extensive search efforts and "if something were to turn up, we're going to be out there, we're going to know it, so I don't want to characterize it as something we have stopped doing."

After waiting expectantly for orders all day in borrowed barracks in this fishing hamlet, state police divers were told late tonight that they had "targets" a few miles southwest and would begin looking for bodies and wreckage at first light.

"It gives the family a sense of closure when you recover someone," Sgt. William Freeman of the Massachusetts Underwater Recovery Unit said in an interview. "That's the only gratifying thing about it. Otherwise, you have to be a very different person to do the job. That's not to say it doesn't bother you."

Hopes for a miracle had dimmed all day, even as a steady stream of leads from a multiagency search condensed the search grid from more than 530 to less than 24 square miles, a patch of the Atlantic Ocean about five miles southwest of Martha's Vineyard.

Spontaneous mourning sites spilled over with flowers from Cape Cod to New York to Arlington as the nation awaited definitive word on the fate of a member of America's first family of politics. The 38-year-old Kennedy's single-engine Piper Saratoga, bound for the Martha's Vineyard airport and carrying his wife, Carolyn Bessette Kennedy, 33, and her sister, Lauren Bessette, 34, had left New Jersey for the island on Friday at 8:38 p.m. and never arrived.

President Clinton, stepping off a helicopter from Camp David this afternoon, referred obliquely to the glamour and pathos linked so long to the Kennedy dynasty, which he said has "suffered much, and given more." In a statement that closed in sad whispering tones, he bade the waiting Kennedys and Bessettes to feel "the strength of God, the love of their friends and the prayers of their fellow citizens."

By then, the Coast Guard's regional commander had conceded that the average crash victim afloat in waters like these clings to life less than a third of the 40 hours that had passed. "Survivability in these water temperatures has been exceeded," Larrabee said, "but those are only statistics." He maintained, for the moment, a formal goal of finding the missing fliers alive.

Later tonight, he prefaced his reluctant conclusion otherwise with the puzzling indirection, to civilian ears, of military speech. "We have begun to look at some of our decision matrix," he said by way of introduction and then stepped through the fundamentals of the case. More than 48 hours had passed. In 68-degree waters, men and women seldom live more than 12 hours "and certainly no more than 18 hours" without life vests or a raft. Careful investigation made clear the plane carried neither. Along the grid of the two-day search, the probability that the ships and planes would have spotted survivors was "as close to 100 percent . . . as we can do it."

Around 4 p.m., an Air Force HC-130 picked up a single ping -- or electronic transmission -- from an underwater transponder and shifted the focus of the search to the seabed about 4 1/2 miles southwest of the island. Larrabee told reporters that he asked a National Oceanographic and Atmospheric Administration vessel, the Rude, to steam at once to the site and direct its sensors in a tight grid around the signal's origin.

That transmission turned out to be a false lead -- probably a signal buoy the Coast Guard itself had dropped -- but fresh sonar images from the Rude led commanders to activate the 10 police divers in Menemsha.

The divers from the Massachusetts Underwater Recovery Unit waited with outward calm for word that their grim specialty would be called upon. Freeman, who said he had "recovered over 100 bodies from drownings or ship sinkings," along with the occasional airplane crash, said he had never known a victim before. He felt he knew these, if not personally. Waiting for news all afternoon, he recalled watching as an eighth-grade student in 1963 as John-John Kennedy, on his third birthday, gave his slain father the famous farewell salute.

At the Vineyard's West Tisbury airport, where a makeshift command center brought authorities together with media from around the world, another Boston trio stood by -- linked by happenstance to tragedy and unwilling now to walk away. Like the missing fliers, they were in their thirties, affluent and attractive, an affianced couple and their close friend. What bound them to the Kennedy party was that they were the first on Saturday to find a piece from the doomed airplane.

Jennifer Maxwell and Damon Seligson, who plan to marry in six weeks, were playing with their basset hound and chocolate Labrador when they saw a large, dark object floating in the whitecaps offshore. With their friend Lauren Belinfante they stood at the water's edge, staring and hoping with heartsick doubt that it would just be trash.

When the shape resolved into a suitcase, Seligson swam out and retrieved it. "My heart started pounding and I was thinking, "Please, don't let it be what I think it is,' " he said. Inside, Mitchell said, were Lauren Bessette's Morgan Stanley Dean Witter business card and "her clothes, still folded neatly." The knowledge of what their find must mean "was horrible, really horrible."

Today they could not tear themselves away from the epicenter of the search. They did not seek out reporters, merely watching from the periphery. But Seligson said that "we just feel invested in this now. We don't feel we can leave."

Using so-called "dry suits" and full-face auger masks with radio gear, the police divers are capable of working at up to 130 feet of depth -- but only for 10 minutes at a time. The sea bottom south and west of here seldom exceeds that but is littered with shipwrecks and unexploded munitions from military accidents.

Apart from bringing back the remains of the missing trio, the divers are capable if asked to use inflatable "lift bags" to return the six-passenger aircraft to the surface.

By Monday afternoon, according to Coast Guard Capt. Russell Webster, the Navy salvage vessel USS Grasp will arrive with a dive team rated for deeper water and heavier lift operations.

At Otis Air Force Base on the mainland, Chairman James Hall of the National Transportation Safety Board said veteran investigator Robert Pearce would head a probe he said could take six to nine months to decide the probable cause of Friday night's crash. Pleading with reporters not to speculate, he said "we are at the very beginning stages of what will be a painstakingly detailed investigation" and "there is even a possibility we will never know."

The National Weather Service reported that haze cut visibility to about six miles at Martha's Vineyard airport, where Kennedy was supposed to drop off Lauren Bessette before heading with his wife to Cape Cod for the wedding of his cousin Rory Kennedy.

But Bob Arnot, chief medical correspondent for NBC, said visibility Friday night was limited by haze as he passed about three miles south of the Vineyard just after 9 p.m. He had to rely on instruments to land at the nearby island of Nantucket, where he vacations.

"It was just black," Arnot said. "You couldn't see Martha's Vineyard."

John McColgan, of Vero Beach, Fla., who was the examiner when Kennedy tested for his pilot's license in April 1998, said Kennedy already had flown about 100 hours when he was tested. He needed only 40 at that point, he said. He said Kennedy postponed the first flight test for a day because of bad weather. "He said, `No, I ain't flying in that stuff,' " McColgan recalled yesterday. He passed easily the next day.

The search day began with the predawn arrival of the Coast Guard cutter Willow, which played a large role in ferreting out the debris of TWA Flight 800 in 1996. The search area was vast, the state of the wreckage probably scattered. "Any time with a plane hitting the water, it's going to come apart," said police diver Richard White. "There is going to be a debris field."

Overhead at Philbin Beach and out to sea from Gay Head, red and white Coast Guard HH-60Js, variants of the Army's Black Hawk helicopter, searched the waves. The HC-130, an Air Force flying command post, turned shallow ovals just offshore, bulging at top and bottom with sensors and communication gear.

This morning, worshipers on Cape Cod offered prayers for two stricken families in the white clapboard churches of Hyannis, where many feel a kind of kinship by proximity with the Kennedy clan. One asked if John's sister, Caroline, had "come home," but while Caroline Kennedy Schlossberg had returned east from a vacation in the western United States, she was staying with her family in the Hamptons on Long Island.

"Why is there evil in this world? Why is there suffering?" the Rev. Edward Byington asked a crowded mid-morning Mass at St. Francis Xavier Church, which has long ties to the Kennedys. "Why, we ask ourselves, this tragedy -- this young man and his wife and sister-in-law cut down in the prime of life?"

As a half-dozen camera crews quietly taped his sermon, the priest went on, "There will come a day when all wrongs are righted."

The carved wooden canopy of the altar was donated decades ago by Rose and Joseph Kennedy in memory of an earlier tragedy, Navy flier Joseph Jr.'s death in a plane accident during World War II. A gilded Navy cross hangs above the altar's crucifix. Maria Shriver and Arnold Schwarzenegger said their wedding vows before it.

Farther down Main Street, at the interdenominational Federated Church of Hyannis, deacon Iris Flynn said she had been praying privately for the family. She had worked as a nurse for matriarch Rose Kennedy. "A very sad day once again," she said, her eyes reddening.

The Rev. James Scovil echoed her thoughts in his sermon. "The local tragedy of these past days reminds us dramatically that the world is not a perfect place. And that the kingdom of heaven is a long way off."

Staff writer Paula Span and special correspondent Pamela Ferdinand in Massachusetts and staff writers Don Phillips and Will Woodward in Washington contributed to this report.

America Reacts

"For more than 40 years now, the Kennedy family has inspired Americans to public service, strengthened our faith in the future and moved our nation forward. Through it all, they have suffered much and given more."

President Clinton

at the White House

"To me, he was Mr. New York. Everybody loved him, and he was a really nice guy. He said hello to me once when I met him riding my bike."

Jose Torre

a TriBeCa neighbor of

John F. Kennedy Jr.

"He was fiercely and proudly a Kennedy . At some point he would have run for office, and I think he would have been extremely good at that."

Robert Shrum

Kennedy family adviser

on CBS's "Face the Nation"

"I was kind of looking forward to him getting into the political forefront."

Todd Taylor

of Myrtle Beach, S.C.,

who was visiting the

John F. Kennedy grave in

Arlington National Cemetery

"We inherited our fathers' and families' friends, and we inherit their enemies. We've earned neither and so we work just as hard, oftentimes twice as hard, to show people that we are who we are, we're real people and we're trying our very best to make a difference."

Jesse L. Jackson

civil rights leader

on "Fox News Sunday"

"He attained a princely status not so much by birth but by bearing. He conducted himself, in an age of incivility, with great civility and great dignity, which incidentally was unpretentious, relaxed, comfortable, confident."

Sen. Joseph I. Lieberman

Connecticut Democrat on

"Fox News Sunday"

"Whether any single Kennedy, or all the Kennedys put together, were ever as good as they are perceived to be doesn't matter. John F. Kennedy Jr. represents an ideal. It is the ideal as much as the man that we mourn."

Andy Rooney

on CBS's "60 Minutes"

CAPTION: A National Oceanic and Atmospheric Administration ship, the Rude, searches the Atlantic near Edgartown, Mass., for missing plane of John F. Kennedy Jr.

CAPTION: A police officer examines debris along the beach in the area of Gay Head, Mass., as a helicopter in the background searches the shoreline of Martha's Vineyard for signs of the plane flown by John F. Kennedy Jr.

CAPTION: Visitors to the grave of President John F. Kennedy at Arlington National Cemetery pay special respects, some placing notes and flowers.