President Kennedy leaned on it during the Cuban missile crisis. His mother found solace in it after gunshots in Dallas. And now the Kennedys seek its sustenance through a grim vigil in Hyannis Port.
Both lightning rod and source of comfort, their Roman Catholic faith has been the spiritual fuel that has propelled the Kennedys through tragedy and turmoil across generations.
A belief that human destiny is ultimately in God's hands - that one's true and eternal reward comes after death - has influenced the way many Kennedys have conducted their lives.
''They know at a deep-heart's level that this life is not the be-all and the end-all,'' said Thomas Groome, a professor of theology and religious education at Boston College. ''You would think that people who have so much money and power and fame would. But they have this genuine faith that for those who have passed on, life has changed - not ended. The Irish wake is as big a celebration as the Irish wedding.''
As a weekend of celebration became cloaked in grief after the news that John F. Kennedy Jr., his wife and sister-in-law were lost in a plane crash at sea, the family used a wedding tent as a makeshift church to celebrate Mass and pray for divine mercy.
''I'm sure that the faith that Rose Kennedy held so intensely is part of her legacy to her children and her grandchildren,'' said Bishop Sean P. O'Malley of the Diocese of Fall River. ''So I'm not at all surprised that in this moment of crisis they are turning to their religion as a source of strength.''
Indeed, in a family that has both absorbed criticism for blurring the lines between church and state and for not strictly observing church doctrine, religion has been a common thread through tragedy and triumph.
''They always come back to that and it seems to give them strength to go on,'' said the Rev. Gerard P. Walsh, chaplain of the Massachusetts State Police. ''They don't exactly wear their faith on their sleeves, but there's no mistaking that it's a central part of their lives.''
Moments after John F. Kennedy became the nation's first Catholic president, he concluded his inaugural address with a promise to ''go forth and lead the land we love, asking His blessing and His help, but knowing that here on earth, God's work must truly be our own.''
In the middle of the missile crisis that brought the United States and the Soviet Union to the brink of nuclear war, Kennedy slipped out of the White House, pausing to pray at St. Matthew's Cathedral near the White House. And in November 1963, when he was murdered by a sniper in Dallas, his mother said the first thing she thought to do was call a priest and ask that a Mass be said for her slain son.
In the aftermath of the assassination, when talk turned morbid, Rose Kennedy told a guest: ''I'm sure God wants us to be happy and take pleasure in life. He doesn't want us to be sad.''
That, observers said, explains the walks on the beach, the afternoon sailing excursions, and driveway basketball games that have unfolded in Kennedy homes from Cape Cod to Long Island as dive teams search for JFK Jr.'s airplane at the bottom of the Atlantic.
If their religion has been a source of strength, it has also stirred controversy.
It bedeviled former US representative Joseph P. Kennedy II in 1997 when his ex-wife criticized the church's decision to annul their marriage.
Senator Edward M. Kennedy was rebuked by Cardinal Bernard Law of Boston in 1994 when the senator said he favored the ordination of woman as priests, bucking the Vatican's ban on that practice. And JFK himself won the presidency in 1960 in the face of considerable religious bigotry.
But through it all, the Kennedys maintained close ties to the church of their matriarch, Rose Kennedy, a daily communicant, whose family paid for the altar at St. Francis Xavier Church in Hyannis in memory of Joseph P. Kennedy Jr.
News of his death in World War II was delivered by two priests at the family's Hyannis Port compound.
''You see in the Kennedys a Catholic ethos that just bites deeply into their being,'' said Lawrence Cunningham, a theologian at the University of Notre Dame. ''If you're going to be a sinner, you're going to be a Catholic sinner. At the moment of crisis, this is the way you can best express yourself. It's deeply cultural.''
Plans for another Kennedy funeral await word on recovery efforts. But officials at Arlington National Cemetery have measured JFK's plot in case the family seeks permission from President Clinton to bury the late president's son there.
And although the presence of a body is central to the Catholic funeral rite - a symbol of the Resurrection - specialists say a funeral Mass can be celebrated without one.
And then the Kennedy family is fully expected to emerge from the church in the spirit that Joseph Kennedy Sr. greeted the news of his namesake's wartime death.
''We've got to carry on,'' his wife quoted him as saying in ''Times to Remember,'' her 1974 autobiography. ''We must take care of the living. There is a lot of work to be done.''