ROME (RNS)--Pope John Paul II wrote a new chapter in the history ofecumenism Tuesday by opening the Holy Door of a major Roman basilicatogether with an Orthodox metropolitan and the Anglican archbishop ofCanterbury.

Then, in a dramatic and unscripted gesture expressing their wish forunity, the two representatives of churches separated from Rome since the11th and 16th century kneeled in silent prayer on either side of thepope at the threshold of the great Byzantine door of the Basilica of St.Paul's-Without-the-Walls.

"Welcome to this encounter, which marks a step forward toward theunity of the spirit in which we have been baptized," the Roman Catholicpontiff said. "Christ, who leads to reconciliation, to peace and tounity, is the door of our salvation."

John Paul addressed delegations from 23 Christian communionsassembled in the basilica for an historic liturgical celebration at thestart of the annual Week of Prayer for Christian Unity. Vaticanofficials said it was the largest ecumenical gathering since the SecondVatican Council of the 1960s.

It also was the first time since the church began celebrating HolyYears seven centuries ago that a pope has himself opened the Holy Doorof St. Paul's and the first time he has shared such a ceremony withprelates of other Christian churches.

For the Great Jubilee of the Year 2000 launching the thirdmillennium of Christianity, John Paul has opened the Holy Doors of allfour major basilicas at the Vatican and in Rome--St. Peter's, St. John Lateran, St. Mary Major, as well as St. Paul's.

The Holy Doors are open only during Holy Years, normally called by apope every 25 years. Pilgrims receive a plenary indulgence--or fullremission of temporal punishment for sins--when they enter thebasilicas through the Holy Doors to pray.

Metropolitan Athanasios of Helioupolis and Theira, representingBartholomew I, ecumenical patriarch of Constantinople (Istanbul) and spiritualleader of the world's Christian Orthodox churches, and George Carey,archbishop of Canterbury and spiritual leader of the worldwide AnglicanCommunion, flanked the pope at St. Paul's 11th century bronze and silverHoly Door, forged in Constantinople in 1070.

"This is the Lord's own door," the pope intoned. "Where the just mayenter," responded the congregation of more than 12,000 people, including25 cardinals and scores of archbishops, bishops, priests and nuns.

As the pope kneeled, the choir and congregation sang, "Christyesterday and today, the End and the Beginning: Christ Alpha and Omega.To him be glory through every age forever."

The ritual had called for John Paul to kneel alone at the threshold,but first Carey and then Athanasios dropped to their knees to join himin prayer.

The ailing 79-year-old pontiff, wearing a cape of gold brocade linedin orange silk, walked unaided down the long aisle of the church andspoke in a strong, clear voice during the two-hour service.

John Paul has made ecumenical dialogue a priority of hispontificate. On Sunday, looking toward the Tuesday service, the popesaid: "We will ask pardon of God and of each other for the sinscommitted against the unity of the church and, at the same time, we willoffer thanks for the path to reconciliation we have covered, especiallyin the last century."

"The wish that gushes from my heart," the pope said in his homily,"is that in the not distant future Christians, finally reconciled, mayagain walk together as one people, obedient to the design of thefather."

Each of the representatives sitting in a wide semicircle in front ofthe altar rose after the homily to exchange the sign of peace with thepope and among themselves.

In other ecumenical gestures during the service, an Orthodox deaconcarried the Gospels, and there were readings from the works of twoeminent non-Catholic theologians--Russian Orthodox George Florovski,who died in Princeton, N.J., in 1973, and German Lutheran DietrichBonhoeffer, who was put to death by the Nazis in 1945.

Orthodox prelates attending the service in addition to Athanasiosincluded representatives of the Greek Orthodox patriarchates ofAlexandria, Antioch and Jerusalem, the Russian, Serb, Romanian, Greek,Polish, Albanian and Finnish Orthodox patriarchates, the Coptic OrthodoxPatriarchate of Alexandria, the Syrian Orthodox Patriarchate of Antioch,the Armenian Apostolic Church, the Catholicosate (patriarchate) ofCilicia and the Assyrian Church of the East.

Representatives of Reformed, or Protestant, churches in addition toCarey included Archbishop Antonius J. Glazemaker of the OldCatholic-Union of Utrecht Church; Bishop Christian Krause, president ofthe Lutheran World Federation; the Rev. Frances Alguire, president ofthe World Methodist Council; the Rev. Richard L. Hamm, president of theChristian Church (Disciples of Christ); Pentecostal leader Cecil M.

Robeck Jr., and Bishop Jonas Jonson of the World Council of Churches.

Together they represent about 80 percent of Christianity.

Those absent included the Protestant Waldensian Church of Italy andthe World Alliance of Reformed Churches, which have refused to take partin Holy Year celebrations to protest the granting of indulgences, a keyissue in the 16th century Protestant Reformation.