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He was the first pontiff in modern times to celebrate Palm Sunday Mass outside of Rome. Now, for the first time in his groundbreaking papacy, an ailing Pope John Paul II (search) was himself expected to be a spectator as throngs of faithful jam St. Peter's Square to usher in Holy Week.

Potted olive trees surrounded the obelisk at the center of the square and row after row of gray plastic chairs were lined up in the vast space in preparation for Sunday's midmorning Mass, which commemorates Christ's triumphant entry into Jerusalem (search).

But in a sign of the extent to which his health has deteriorated, John Paul won't be presiding over one of his favorite ceremonies, which marks the start of the most important week in the Roman Catholic liturgical year. The week culminates with Easter (search) on March 27.

The pope designated Cardinal Camillo Ruini, his vicar for Rome, to lead Palm Sunday Mass.

"It will be an unusual opening, that of Holy Week" without the pope at Palm Sunday Mass, Vatican Radio said.

The Vatican said Friday that John Paul was expected to appear at his studio window on Palm Sunday. But it wasn't clear if he might speak to pilgrims and tourists in the Square.

Accepting the advice of his doctors, John Paul's only Holy Week commitment is an Easter Sunday blessing, while he regains strength at the Vatican after being hospitalized twice in a month with breathing problems. He was released from the hospital a week ago.

John Paul has only been heard speaking publicly twice — each time just a few sentences delivered in a raspy voice — since he had a tube inserted in his throat during surgery on Feb. 24 to ease a breathing crisis. Parkinson's disease, which affects muscle control, also makes it difficult for him to speak clearly.

"I think the faithful are going to be very disappointed but there is nothing they can do. It's life, even if it's sad not to see him on a very special week for the Church," said Gordon Bland, a 79-year-old retiree from London who was in St. Peter's Square with his wife on Saturday.

A top Vatican cardinal insisted Saturday that doctors were hopeful about the 84-year-old pontiff's health.

"The Holy Father is hanging in there, hanging in there," Cardinal Giovanni Battista Re, an Italian who heads the Vatican's Congregation for Bishops, told reporters in the southern town of Campobasso. "The doctors above all are optimistic, and this is a beautiful thing, a good sign."

Twenty years ago, John Paul started dedicating Palm Sunday to young people, whom he cherishes as the future of the Church.

In 1987 he became the first modern pontiff to celebrate the day outside of Rome when he led nearly 1 million people at the ceremony from an altar atop a three-story-high platform down the middle of a boulevard in Buenos Aires.

In the last several years because of frail health, the pope already had scaled back some traditions. He no longer carried the cross during Good Friday Colosseum procession, but sat and prayed.

Yet John Paul has heartened the faithful by bouncing back at times. Last year on Palm Sunday he clutched a braided palm as a symbol of hope and peace and kissed babies held out to him during a drive around the square in an open-sided popemobile.

"I hope that the pope will last a long time, even though with his illness he's teaching us a lot," said Cristian Fanton, one of 200 pilgrims from Brescia, Italy, for Palm Sunday. "I hope after him, they will be able to find someone who is just as charismatic.

Last year on Palm Sunday, the pope urged young people to attend the August 2005 World Youth Day in Cologne, Germany. The trip to Germany is the only scheduled foreign pilgrimage for John Paul this year, but it is not known if he will travel there after his medical setbacks.

In mid-January, the Vatican released a Holy Week schedule, with the pope leading the Palm Sunday celebration. After his hospitalizations, the schedule was changed.