For the generations who saw some kind of magic in the Kennedys, the very name of the town where this rambling, rambunctious family came to escape the public eye represents casual confidence, windswept joy. Hyannis Port. Where a president and senators, sharp-jawed men and strong-boned women, played touch football and raised children to be important people.

Now, once again, Hyannis Port becomes an American Valhalla.

A clan that has been swept mercilessly to and fro between accomplishment and devastation stood yesterday amid the sweetest of decorations, ready to celebrate the unity of two, only to face the possibility of more loss.

At 6 o'clock last night, Rory, a producer and documentary director, was to have wed Mark Bailey, a writer and editor of books and film, before 275 guests, including the only son of the late president. The Kennedy cousins, the loyal friends, the extended family gathered on the broad lawns, the white peaks of wedding tents still looming.

But instead of a wedding, the Kennedys and their guests celebrated a Mass Saturday on the porch of Ethel Kennedy's house. About 50 family members and three priests joined in the prayers "for the safety of the loved ones, as well as for Rory and Mark," said Brian O'Connor, a family spokesman.

"There are a lot of people in the family who don't see each other too often," O'Connor said. "They're still catching up. A somber mood is going on. Mrs. Kennedy is showing great spirit and pulling everyone together. She is the leader in this household."

Friday night had been electric with anticipation. "It was just wonderful over there last night, just exciting," said Christina Rivers of Hyannis, who was to style the hair of the bridal party. "It's just not fair. I don't know what it is, but it's not fair."

Even in the annals of Kennedy tragedies, Rory Kennedy's life stands out. Her mother, Ethel, was pregnant with Rory when Robert F. Kennedy was assassinated in a hotel kitchen 31 years ago. And it was Rory who held her brother Michael as he slipped away, crushed in a New Year's Eve skiing accident in 1997.

Yet she had that irrepressible Kennedy style: She named her New York film company Moxi Firecracker.

On this day of prayer and waiting, the windows of the houses on the Kennedy compound remained shuttered against the eyes of the encroaching world. A hammock, empty now, swung on the front porch where Mass was said.

On a hazy and humid day when vacationers packed nearby beaches, television crews and reporters from around the world lined the entrance to exclusive Marchant Avenue, with its white picket fences and tidy flowering gardens. Neighbors watched the familiar scenes silently, as though reliving last year's Kennedy tragedy in their minds, while police officers guided traffic and dozens of curious Camelot followers flocked to the site, keeping vigil for hours.

Mary Earl, 55, remembered the days when a young American president summered on the Cape and how she watched generations of Kennedy weddings and funerals.

"The day JFK was shot was the worst tragedy. This will probably be the second," said Earl, who lives in nearby Sandwich and spent most of her day outside the compound. "It's just hard to leave. I know I'll go home and watch it on TV. Just being here helps."

It was here that the family has gathered time and again to mourn, to make sense of the impossible, to cherish the fantastic. The members of the nation's most public of families have managed to keep Hyannis Port in good measure to themselves, a place known in the popular mind only as "the Kennedy compound," with only a few carefully chosen images of lawn and porch to bring that phrase to life. Here, the Kennedys have assembled after the election victories and the assassinations, the car crashes and the drug overdoses, the paparazzi assaults and the public scandals.

And now this, the apparent loss of John-John, the nation's favorite toddler, who had grown up and seemed to find his own way despite his heavy burden. The pain, the ironies, do not cease: Some of the first pieces of debris from Kennedy's plane were found near Gaylord, Jacqueline Kennedy Onassis's house at Martha's Vineyard.

John Kennedy Jr. had fought all his life to carve out some form of normalcy, to be something other than the little boy saluting his fallen dad. "It's hard for me to talk about a legacy or a mystique," he said once. "It's my family. It's my mother. It's my sister. It's my father. We're a family like any other. We look out for one another. The fact that there have been difficulties and hardships, or obstacles, makes us closer."

At Hyannis Port, florists and caterers drove into the compound throughout the day, interspersed with shuttles carrying wedding guests whose starched tuxedos and formal gowns hung flat against car windows.

At least one innkeeper had to break the news of the accident this morning to newly arrived guests who happened to mention they were in Hyannis Port to attend a wedding. One neighbor carried a glass vase of lilies and roses into the compound, while another handed a telegram to a security guard standing outside.

Family members could be seen strolling down to the pier from their white clapboard house with green shutters. Former representative Joseph P. Kennedy II returned to the house with his wife late in the afternoon. Sen. Edward M. Kennedy, for so long the flawed and brave substitute patriarch of the clan, once more was tossed into the role of father to so many.

A family spokesman said the wedding has been indefinitely postponed.

At the Sheraton Hyannis Resort, grim-faced and casually dressed guests, one carrying a Bible, began arriving about 7:30 last evening for what was described as a small dinner for the bridegroom's family. About a dozen tables were simply set with burgundy and white table linens and flickering white candles -- no flowers. Reporters were quickly shooed away.

Ferdinand reported from Hyannis Port, Fisher from Washington.

CAPTION: At left, Joseph P. Kennedy II, left, and Housing Secretary Andrew Cuomo, center, with others at Kennedy compound in Hyannis Port. Above, Rory Kennedy.

CAPTION: Rory Kennedy and Mark Bailey, whose wedding was postponed, stroll along beach in front of Kennedy compound in Hyannis Port. Above, Rory Kennedy.