An extended holiday truce in El Salvador, traditional services in Rome and in the Holy Land, and new opportunities to worship in China marked the opening of Christmas celebrations around the world yesterday and early today.

For the families of hostages in Lebanon, however, there were no suggestions that a holiday reunion was in the offing.

Celebrating midnight mass yesterday in St. Peter's Basilica, Pope John Paul II told the throng and "all the peoples and nations," to sing the song inspired by the birth of Christ "that proclaims the divine meaning of human life." The mass was attended by pilgrims from Europe, the United States and Latin America and was broadcast to 30 countries.

Today, the pope will issue a traditional message to the city of Rome and to the world, the urbi et orbi message.

Pilgrims from Europe and the United States, including sailors from the U.S. 6th Fleet, celebrated Christmas Eve at Shepherds' Field, in the Israeli-occupied West Bank near Bethlehem, where tradition says shepherds first heard of Jesus' birth.

The Rev. John L. Peterson, a Baptist minister, led Christmas prayers on the open, rocky field. "Today," he said, "as it was then, there is a hope for peace. That is what this night is all about."

Both Protestant and Roman Catholic services are given on the one-acre plot each year. This year, one of the worshipers said: "It looks like the shepherds are well armed against the wolves," referring to the Israeli soldiers overseeing the services.

"There is an air of peace blowing in our region," Israeli Prime Minister Shimon Peres said at a reception given by Bethlehem Mayor Elias Freij, a centrist Palestinian leader.

In Peking, Catholics are celebrating Christmas publicly for the first time in 27 years. Yesterday night, thousands of Catholics attended midnight mass in the Cathedral of Our Savior, a newly restored church that was closed down in 1958 by Maoists.

The 99-year-old cathedral's midnight mass was celebrated by the Bishop of Peking, Fu Tieshan, primarily in Latin except for a few hymns, including "Silent Night" and "O, Come All Ye Faithful."

Bishop Fu entered the German Gothic-style church dressed in white vestments beneath a canopy held by four choirboys and carrying an image of the Christ child on a green velvet cushion.

Earlier in the day, worshipers crowded into the cathedral for its consecration. The church is the third to reopen in Peking since 1980, when China lifted a ban on religious activities. "This is a wonderful night for us all," said a worshiper.

Salvadorans were surprised when President Jose Napoleon Duarte agreed yesterday to a 10-day holiday cease-fire, the longest ever called in El Salvador's six years of civil war.

The cease-fire was proposed on Sunday by Roman Catholic Archbishop Arturo Rivera y Damas, and the rebels immediately accepted it.

Today's announcement by Duarte said: "On the basis of Christmas spirit and the request of the Salvadoran Catholic Church, the government of the republic decided to suspend offensive actions of the armed forces during the Christmas period."

The statement added, however, that the military "will remain vigilant" during the truce, which began at midnight yesterday and is set to last until Jan. 2. In recent years, truces have been observed for Christmas and New Year's days only.

Anglican Church envoy Terry Waite, who has been negotiating in Beirut for the release of American hostages, hoped to secure a Christmas release but returned to London with only minor progress to report.

Waite said, "I think there is a possibility of a really constructive development" involving proposals that he made to the Shiite Moslem captors in new secret meetings in Lebanon.

Waite also said he had given the kidnapers letters and Christmas cards for the hostages from their families and friends, and advised the families "never to give up hope."