A Dec. 25 article incorrectly reported that the Holy Door opened by Pope John Paul II at St. Peter's Basilica on Christmas Eve had last been opened by Pope Paul VI in 1975. John Paul had also opened the door in 1983, at the start of the 1983-84 Holy Year. (Published 01/05/2000)

Pope John Paul II welcomed tens of thousands of pilgrims to Rome early this morning to mark the start of a yearlong celebration of the 2,000th anniversary of the birth of Jesus that the church hopes will reawaken spirituality for the next millennium.

At a 1 1/2-hour Mass beginning at midnight on Christmas Eve in St. Peter's Basilica, the pope hailed the celebration as a link between contemporary experience and ancient history. He said it gives citizens all over the world an opportunity for redemption from sin during one of the jubilee years that the Roman Catholic Church observes at 25-year intervals.

"It is the solemn beginning of the Great Jubilee. We are spiritually linked to that unique moment of history when God became man," said John Paul in a brief and halting sermon from a lectern at the basilica's high altar.

Beneath him was the tomb of St. Peter, the Galilean fisherman who became head of the apostles and established the papacy in Rome; above him was the basilica's great dome designed by Michelangelo.

Reciting words written more than 1,900 years ago by the apostle Luke and intoned annually before millions of Christians at midnight Christmas services around the globe, the pope told the faithful what an angel of the Lord said to shepherds gathered near the site of Jesus's birth in Bethlehem: "Be you not afraid, for behold, I bring you good news of a great joy. . . . to you is born this day in the city of David a Savior."

"Ever since Bethlehem, humanity knows that God became man. He became man in order to give man a share of his divine nature," the pope said.

For the 79-year-old Polish prelate, whose given name is Karol Wojtyla, presiding over the Mass represented a personal triumph of sorts. His health has been deteriorating since a colon tumor was removed in 1992, and he suffered several major bone breaks. His speech and movement have been slowed by what is believed to be Parkinson's disease.

The pope has often expressed his determination to inaugurate remembrances that the church has designed to promote new spirituality among Christians and help convert more people to Catholicism, particularly in the Third World. He also has sought to use the jubilee as a reason to reexamine the church's history and redeem some of its mistakes, including the cruelty of Christian crusades against Muslims in the Middle Ages and failure to speak out more forcefully against slavery and the abuses against Jews in Nazi Germany.

The pope began the anniversary ceremony by walking into Christendom's largest church through a small portal adjacent to the main door, an opening symbolizing the passage from sin to grace via the spiritual embrace of Jesus's teachings. The portal, dubbed the Holy Door, is only used during jubilee celebrations and was last opened by Pope Paul VI in 1975.

African horns sounded--in a bow to the church's search for new converts on that continent--shortly after the pope walked into a blazingly illuminated basilica carrying a copy of the New Testament, and the crowd packed into St. Peter's Square applauded. The pope then walked slowly down the center aisle, preceded by cardinals and lay Catholics from Europe and America as he passed an estimated 8,200 devotees who won seats sought by more than 60,000 applicants. Viewers around the world watched on television as the choir chanted scriptural verse and the Mass began.

Outside, tens of thousands of pilgrims and tourists made a festive crowd in front of the resplendent basilica, its newly restored facade bathed in light from the steps to the dome. Dozens of beams of light lit a huge nativity scene--42 feet tall by 60 feet wide.

Some were there for a mix of religious sentiment and curiousity. "It's the last Christmas of the millennium and I wanted to make sure to see this pope," said Jeff Cruz, 20, of Lombard, Ill.

Those attending were the first wave of what church officials hope will be more than 20 million pilgrims to come to Rome in the coming year to participate in the anniversary celebration. The city, which has been linked with the Catholic Church for most of both millennia, has been preparing for the influx since 1997, repairing more than 70 of its great houses of worship and undertaking other civic projects.

In his sermon--pared of his customary references to contemporary international affairs--the pope said, "We are witnesses of that instant of love which unites the eternal to history: the 'today' which begins the time of jubilation and hope."

Addressing the spirit of Jesus, he said, "In an ineffable way, your birth has changed the course of human events. This is the truth, which on this night the church wants to pass on to the third millennium."

In timing the anniversary celebration for 2000, the Vatican had to bend the calendar a bit. Although the precise date of Jesus's birth is not known, most religious scholars agree that Jesus was born as early as four to six years before the moment presumed in the modern calendar established by Pope Gregory XIII in 1582.

The Gregorian calendar, derived from another Roman calendar organized a millennium earlier to mark the "year of our Lord" since Jesus's birth, was actually a compromise between science and religious preference, scholars say--a pattern also followed in the Vatican's timing of the present celebrations.

"The date of the millennium is of course symbolic," said the Rev. Georges Cottier, who as Vatican theologian assists the pope with theology and doctrine. "We know that Jesus was born six or seven years before the date that is accepted for his birth. That date is due to a mistake in calculation in the Middle Ages that then was passed on to the calendar.

"But there is no reason to change. We keep it because of the liturgical tradition. We don't give it much importance," Cottier said. "The idea of the jubilee isn't Christian, but comes from the Hebrews, and it means joy and happiness. For Christians, it's a great call to conversion, in a personal sense, an interior step to God and away from sin. It is also a moment for Christians to participate fully in works of charity and justice, especially toward the poor."

The church says that those who make the journey to Rome to seek indulgences, or exoneration, next year are repeating the same journey undertaken in 1300, at the first jubilee, by such pilgrims as Dante Alighieri, the artist Giotto and the family of the King of France.

The largest crowds are expected to come to Rome to celebrate Easter on April 23, to attend a congress of Christians on May 1 and a conference on families on Oct. 15. The church also predicts that up to 2 million young people will attend a meeting on the outskirts of Rome on Aug. 19 and 20.

Special correspondent Sarah Delaney contributed to this report.