Vatican City ? An ailing Pope John Paul II celebrated his 25 years as pontiff on Thursday, asking tens of thousands of pilgrims, his admiring Polish countrymen and the men who help run his church to pray for him, saying his future rested in the hands of God.

The festivities, made bittersweet by the pope’s obvious ailments, highlighted John Paul’s role as one of the most influential religious figures of the last century as he reached a milestone matched by only three of his predecessors.

At least 50,000 people packed St. Peter’s Square for an anniversary Mass that began at 6 p.m. — about the same time a quarter-century ago that white smoke from a Vatican chimney signaled that a Polish cardinal named Karol Wojtyla had been elected the first non-Italian pope in 455 years.

As the sun set over the square, the crowd broke into applause when a weary-looking John Paul was wheeled to the altar, dressed in golden vestments and a jeweled miter, while a choir sang hymns.

He smiled after the greeting from the dean of the College of Cardinals, Cardinal Joseph Ratzinger, who praised the pope for his tireless work and his endurance of “criticism and insults.”

“You turned to young and old, rich and poor, powerful and humble, and always showed, according to the example of Jesus Christ, a particular love for the poor and the defenseless,” Ratzinger said.

The 83-year-old pope, who suffers from Parkinson’s disease, read only portions of his prepared remarks, including a prayer, and appeared pained at times. He spoke in a strong voice during his homily, but began slurring his words later in the two-hour service.

Pope John Paul II recites Mass during his 25th anniversary at St. Peter's Square at the Vatican. Tens of thousands of pilgrims streamed into St. Peter's Square Thursday for the two-hour Mass, which stretched the ailing pope's endurance.

“I renew, in the hands of Mary, beloved Mother, the gift of myself, of the present and the future: everything will be done according to your will. Supreme Pastor, stay among us so that we can proceed with you securely to the house of the Father.”

And in a portion read by an aide, John Paul said, “Help the pope and all those who want to serve Christ.”

As the Mass ended on a floodlit square, John Paul asked for a closing hymn dedicated to the Virgin Mary, for whom he has always had a devotion.

Official congratulations poured in from overseas.

“The United States and the world are better because of his dedication to sharing his wisdom, guidance and faith,” President Bush said in a statement saluting the pope.