(RNS) VATICAN CITY -- Greeting the new millennium with an appeal for peaceand a party for tens of thousands of children, Pope John Paul II hasembarked on a crowded Jubilee schedule that will test his endurance tothe limit.

The Christmas and New Year's festivities were only the start of ayearlong calendar of Holy Year events for the 79-year-old Roman Catholicpontiff, who wages a constant battle against the debilitating effects ofa neurological ailment.

John Paul plans at least one pilgrimage to the Holy Land this yearplus scores of special meetings with Holy Year pilgrims expected toflock to Rome and the Vatican by the hundreds of thousands.

The Vatican's Central Committee for the Great Jubilee of the Year2000 has scheduled mass pilgrimages by the sick, the elderly and thedisabled, as well as artists, artisans and workers, scientists,immigrants, journalists, families, athletes, politicians, farmers,soldiers and university professors.

The pope also will preside over beatifications and canonizations inSt. Peter's Square, and he will visit Rome's Rebibbia Prison for a HolyYear celebration with prison inmates.

The Vatican welcomed its first mass Holy Year pilgrimage on Sunday(Jan. 2) when a crowd of some 150,000 adults and children gathered inSt. Peter's Square and on the wide avenue leading from the Tiber Riverto the square for a children's jubilee.

"There are so many of us you can't see where it ends, perhaps to theTiber and beyond," a smiling pope commented."You belong to the third millennium, not the last one," John Paultold some 50,000 children, ages 6 to 14, who had traveled to the Vaticanfrom 30 countries. Among them were 10 former child soldiers rescued bythe church in Sierra Leone.

Speaking in Italian, French, English, Spanish and his native Polish,John Paul deplored poverty, violence and the exploitation of childrenand attacked artificial birth control and abortion.

"At the beginning of a new year, dear children and young people, wecannot forget all those of your own age who are suffering hunger orviolence and those who are victims of hideous forms of exploitation," hesaid. "How can we forget the many children who are denied even the rightto be born?"

Two days earlier, at a New Year's Eve Te Deum Mass of Thanksgivingin St. Peter's Basilica, John Paul singled out the discovery of Americaand the rise of fascism and communism as major events of the millenniumand the century drawing to a close.

"The discovery of America, which gave the start to a new era in thehistory of humanity, constitutes without doubt a key element in theevaluation of the millennium that closes today," he said.

"This last century was characterized by deep and at times rapidupheavals that affected the culture and relations among peoples. It isenough to think of the two oppressive ideologies, responsible forinnumerable victims," the pope said. "What suffering and what dramas.But also with exalting conquests."

On New Year's Day, John Paul drove across the Tiber to the 13thcentury Basilica of St. Mary Major atop the Esquiline Hill to mark thechurch's 32nd Annual World Day of Peace. He formally opened thebasilica's Holy Door and celebrated Mass.

In his homily, the pope recalled the meeting he held in 1986 withrepresentatives of the world's principal religions at St. Francis'birthplace of Assisi to pray for an end to the threat posed to humanityby the Cold War.

"Although we have had to note the outbreak of perilous local andregional conflicts, we nevertheless have been saved from the worldconflict that appeared to be on the horizon," he said.

The pope returned to the theme of peace during the Sunday (Jan. 2)Angelus prayer from his study window. "An invocation of peace rises inchorus from every part of the world," he said. "We pray that it does notfall unheard. In this moment, my thought goes to the many victims ofviolence, to those who feel alone and abandoned."

On Thursday (Jan. 6), John Paul will mark Epiphany--the 12th dayof Christmas and the arrival of the Magi at Jesus' manger--byconsecrating newly elevated bishops and archbishops. On Sunday (Jan. 9),the Feast of Jesus' Baptism, he will baptize a group of infants.

The holiday observances will close Monday (Jan. 10) when the popedelivers an address on international issues at his New Year audience fordiplomats from more than 150 countries accredited to the Vatican.