Pope John Paul II offered his prayer for a new millennium "filled with joy and peace" in a midnight address to tens of thousands of exuberant Romans and tourists gathered in St. Peter's Square to hear a pop music concert organized by the Vatican to help ring in the new year.

After the clock struck midnight and fireworks lit the sky behind St. Peter's Basilica, the pontiff appeared at the window of the papal apartments adjacent to the basilica and issued his traditional New Year's blessing: "The clock of history strikes an important hour," he said. "For believers, this is the year of the Great Jubilee," a time when pilgrims and those who perform charitable acts can gain exoneration from sin.

The pope's declaration, which prompted prolonged cheers from the 120,000 people gathered below, came in the middle of a two-hour performance by one of Italy's best-loved romantic singers, Claudio Baglioni, and gospel singers led by an American soloist, Queen Esther Marrow.

"As we cross the threshold of the New Year, I would like to knock at the door of every home, to bring to each of you my cordial good wishes: a happy new year to everyone in the light which shines out from Bethlehem upon the whole universe," said the ailing pope, who has openly looked forward to the millennium celebration ever since his election 21 years ago.

"I wish you a year filled with peace: the peace proclaimed by the angels" on the night of Christ's birth, the pope said in his upbeat message. "May you always be certain of God's love for us. . . . Let us enter the year 2000 with our eyes fixed on the mystery of the Incarnation."

Earlier in the evening, after the pope said Mass inside St. Peter's, pilgrims and concertgoers milled around the square and the brightly illuminated basilica, its facade shining from a just-completed restoration. Sonia Gallotta, 21, a student from Sassari, Sardinia, said that she and three friends had come mostly for the music "but also because we knew we could see the pope" in his midnight blessing.

"It's a historical place to spend New Year's, and there's something special about this one. I'm hoping for peace, especially after last year's war," Gallotta said.

Francesca Talarini, 28, of Tivoli, east of Rome, said, "We came to see the restoration, but also because we wanted to spend New Year's Eve here. You always expect something different with the new year, and this time even more so because it's the new millennium."

At the service, the pope, dressed in white vestments, was wheeled down the aisle of St. Peter's standing on a platform that he used for the first time Wednesday. While he was unable to shake hands with worshipers in the church, as he usually does at the end of a Mass, the platform saved him from repeating what seemed to be a long and difficult walk down the aisle to welcome the jubilee year on Christmas Eve.

The pope, 79, suffers from a Parkinson's-like disease that makes walking and climbing stairs difficult.

In his sermon, the pope had somberly asked those in the audience to remember some of the past millennium's errors as well as its triumphs. He mentioned in particular "two oppressive ideologies"--presumably communism and Nazism--that he said could be blamed for "innumerable victims" and much suffering.

Striking a favorite theme, the pope also said the epoch's greatest challenge remains the identification of "perennial values" that must be harmonized with contemporary discoveries.

"As we lift our thanks to God, we feel the need to implore, at the same time, mercy for the millennium that is closing. We ask for forgiveness because not rarely, unfortunately, scientific and technical conquests, so important for the authentic progress of man, are used against man," the pope said.

Although some Romans have criticized the Roman Catholic Church for organizing most of the jubilee events here, the secretary general of the Vatican's jubilee committee said the events were meant to be inclusive. "The Holy Year does not only affect Catholic pilgrims . . . but also believers of other Christian confessions, different religions, and even those who do not believe," said the Rev. Creszenzio Sepe.

He added, "Today's society, precisely because it is apparently so arid and materialistic, in reality expresses a strong need for spirituality and transcendence," one of the principal themes of jubilee years declared by the Vatican every 25 years.

CAPTION: At midnight, from the window of the papal apartments adjacent to St. Peter's Basilica, Pope John Paul II addresses tens of thousands of listeners in the square below.

CAPTION: Fireworks light up the sky above St. Peter's Basilica, where the pope offered a midnight prayer and expressed his hope for peace. The pope's address came in the middle of a pop music concert organized by the Vatican.