Against a backdrop of war, terrorism and Mideast tensions, Pope John Paul II celebrated a somber Christmas Eve Mass, praying for salvation and urging the faithful to become "builders of peace."

The pope, appearing in good form, ushered in one of Christianity's most joyous holidays by recalling the "relentless news headlines" of recent days during his midnight Mass homily inside St. Peter's Basilica.

"Our hearts this Christmas are anxious and distressed because of the continuation in various parts of the world of war, social tensions, and the painful hardships in which so many people find themselves," the pope said, his voice strong and clear.

"We are all seeking an answer that will reassure us."

As St. Peter's twinkled from flashbulbs and floodlights, police outside searched pilgrims' bags and purses and used metal-detecting wands as part of the Vatican's anti-terrorism security.

While the Italian media have said the Vatican is a prime terrorist target following the Sept. 11 attacks, the security measures resembled those taken during the past two Christmas holidays, which flanked the Vatican's Holy Year celebrations that drew millions of pilgrims to Rome.

John Paul opened the day's celebrations by lighting a single Christmas candle in the window of his apartment overlooking St. Peter's Square — a silent vigil for peace that has been a hallmark of his 23-year papacy.

Out in the bone-chilling cold of the piazza, bands played Christmas carols as a life-sized creche was unveiled next to a 80-foot-tall Christmas tree decked with gold and silver balls. Church bells heralded the start of the Mass and a boy's choir sang.

Despite the joyous scene, the weight of the world's woes cast a shadow over the Vatican as it marked the birth of Christ.

The Vatican announced Monday that an appeal to the faithful to fast on Dec. 14 in the name of peace and to donate money instead to victims of terrorism raised $650,000 in donations.

The Vatican also said it had taken diplomatic steps to try to head off what it called the "arbitrarily imposed" decision of Israel to block Palestinian leader Yasser Arafat from attending midnight Mass in Bethlehem, the birthplace of Jesus.

Israel has said it would only let Arafat travel there if he arrested the killers of an Israeli Cabinet minister.

Vatican spokesman Joaquin Navarro-Valls didn't elaborate, but the pope has previously spoken out about the sanctity of Bethlehem and the Holy Land and has frequently urged both sides to work for peace.

The pope didn't mention the Sept. 11 attacks in his homily — but he said current events dimmed the joy and light that the faithful should feel on Christmas.

"If we listen to the relentless news headlines, these words of light and hope may seem like words from a dream," he said. "But that is precisely the challenge of faith, which makes this proclamation at once comforting and demanding."

He urged the faithful to draw power from God's love to overcome the world's iniquities by "becoming witnesses of solidarity and builders of peace."

The traditional Mass moved back inside St. Peter's Basilica after a one-year stint outdoors in St. Peter's Square. The pontiff celebrated Christmas Eve Mass outdoors last year to accommodate the hundreds of thousands of pilgrims who flocked to Rome during the Vatican's Holy Year celebrations.

On Tuesday, the pope is to deliver his traditional Christmas day message followed by greetings in dozens of languages to pilgrims in St. Peter's Square.