VATICAN CITY, Dec. 24 (AP) - Wishing ``Merry Christmas to all,'' Pope John Paul II on Sunday opened the celebrations that will take his church to the end of the 2000 Holy Year by greeting pilgrims who stood in a bone-chilling drizzle in St. Peter's Square.

With the main appointment John Paul's celebration of Christmas Eve Mass in St. Peter's Square, the day held events heavy in symbolism, including homeless men bringing sleeping bags as the first gift for the Christ child in the life-size nativity scene being unveiled in the square later in the day.

``This scene, in its simplicity, constitutes a silent invitation to understand in its true value the mystery of Christmas, a mystery of humility and of love, of joy and of attention to poverty,'' John Paul said in a noon appearance at his window over the square, where thousands of pilgrims, bundled up, were waiting to see him.

``While in the houses all put the last touches on the nativity scenes and prepare to pass Christmas in serene family harmony, don't leave out a gesture of solidarity to those who, unfortunately, live these days in solitude and in suffering.''

The 80-year-old pontiff's voice at times sounded snuffly, as if he might be coming down with a cold, but it rang out strong over the crowd of faithful.

After days of brilliant blue skies, Christmas Eve day in Rome dawned gray and cold, forcing shopping throngs to dig out hats and gloves which had so far gone undonned.

In past years, John Paul celebrated midnight Christmas Eve Mass inside the basilica, but with Holy Year crowds eager to see the pope, the event was being held in the square despite the damp cold.

Italians planned traditional gifts for the nativity scene, from a model Boeing 747 from state airline Alitalia to the homeless men's sleeping bags to soccer shirts for the Christ child from Italian stars Francesco Totti and Gabriele Batistuta.

The Roman Catholic Church's 2000 Holy Year, one of the crowning events of John Paul's papacy, now in its 23rd year, ends on Epiphany, Jan. 6.

Then, John Paul will preside over a ceremony which will lead to the bricking up of the holy door of St. Peter's Basilica, symbolically closing a year that brought almost 25 million pilgrims to Rome.

Among the square's features is a Christmas tree donated by Austria's southern Carinthia province, which is headed by far-right leader Joerg Haider. His visit to the Vatican earlier this month to present the tree triggered several protests, including clashes in which police lobbed tear gas at demonstrators near St. Peter's Square. Since then, police have been guarding the tree.