VATICAN CITY, DEC. 25 -- Warning that "war is an adventure with no return," Pope John Paul II admonished world leaders on Christmas Day to settle the Persian Gulf crisis peacefully through negotiations.

Thousands of chilled pilgrims silently stood in a wet and cold St. Peter's Square to hear the pope's powerful appeal for peace in "the tormented nations of the Middle East."

If the rainy weather cut the size of the crowd, the tenor of the papal message and John Paul's unusually blunt language also stole much of the festive air from the annual gathering in the giant Renaissance square before St. Peter's Basilica.

"For the area of the gulf, we await with trepidation for the threat of conflict to disappear," John Paul said. "May leaders be convinced that war is an adventure with no return."

The statement was John Paul's strongest plea for peaceful settlement in the gulf since Iraq's Aug. 2 invasion of Kuwait, which the pope condemned.

Noting that the message was delivered on Christmas, which the world's 850 million Roman Catholics celebrate as the birthday of "the prince of peace," observers here read the appeal as a stark expression of the Vatican's fear that war is near, and its conviction that violence can be headed off by negotiations.

Archbishop of Canterbury Robert Runcie, leader of the world's 70 million Anglicans, referred in his last Christmas sermon before he retires next month to the specter of a "fearsome combat" in the gulf. He prayed for the safety of troops there, as well as for the people of Kuwait.

In Bethlehem, the traditional birthplace of Christ that has been under Israeli military occupation since 1967, heavy security and a sense of foreboding over the region's future meant only a few hundred worshippers celebrated midnight Mass in St. Catherine's Church.

In a somber sermon, the Latin patriarch of Jerusalem, Michel Sabbah, appealed for love and justice "on the eve of an imminent world war."

"It is the saddest, gloomiest Christmas I remember in my lifetime," said Elias Freij, Bethlehem's Palestinian mayor.

But in a few places, the Christmas message of peace and tolerance managed to shine through the gloom.

For his own European continent, the Polish-born pope was upbeat, hailing the "demanding challenges and prospects" of a new Europe being forged "above the tumbled walls of ideological and political opposition." He warned Europeans, though, that they must overcome "hedonism and practical materialism" if the barriers between them are to be erased.

In Berlin, hundreds of Germans opened their homes to Soviet soldiers who will soon evacuate the region they controlled as an occupation force for 45 years.

"It's a very special, unprecedented day for us, like a big Christmas present," said one soldier.

About 380,000 Soviet troops are to be withdrawn from eastern Germany by 1994, and Germany is airlifting food and other goods to the Soviet Union to tide it through a harsh winter of shortages.

In Albania, an estimated 10,000 Christians attended their first Christmas Mass in 23 years in the northern city of Shkoder. The service was made possible by President Ramiz Alia's decision last month to lift a ban on religion imposed by the late Stalinist leader Enver Hoxha.

In the central African country of Congo, which recently abandoned its official Marxist dogma in a wave of political change, religious broadcasts were heard on state media for the first time in 12 years.

Congolese television broadcast a midnight Mass from Brazzaville's Roman Catholic cathedral Monday night while radio carried a Protestant service. Radio and television have been playing Christmas carols since Monday.

In China, an officially atheist country, worshipers and the curious joined in prayer and song in state-controlled churches.

"I am not a believer," said one student who attended a service in Beijing, "but I know this day is very important to some people here and people everywhere. I just want to learn a little about it."