MANILA, Philippines -- In Denver 17 months ago, in a World Youth Day gathering that many people compared to Woodstock, Pope John Paul II enthralled young Americans packed into a park in a scene that had all the backpack- and blue-jean bonhomie of a 1960s rock concert.
Yesterday, it was the pope's turn to be impressed.
On the first World Youth Day gathering since the one in Denver in August 1993, up to 4 million people turned out yesterday in the Philippines, the Vatican said, and many clerics said it was the biggest audience the pope had ever seen at a papal Mass.
People crammed routes leading to the vast Luneta Park along the seashore. They spilled 50 deep from the sidewalks, which were so densely packed that the pope was forced to abandon his armored, glass-sided vehicle and to use a helicopter to avoid the crush.
People clambered onto rooftops, cars and scaffolding to get a better view, and many of them who did not get close said they still felt close to him. "Even though we won't see him, we can feel his presence," said Lydia Angeles, 58, whose 6-mile trek to see the pope ended 500 yards away behind a wall of people.
Hundreds fainted. More than 1,000 people were treated for dehydration.
By Saturday night, when the pope swayed with them in song at a prayer vigil in Luneta Park, their numbers had swelled from an estimated half-million to a million, including the 450,000 young delegates to World Youth Day.
Overnight, hundreds of thousands more pushed the figure to about 2 million. It was already such a throng that bishops were roused from their beds at dawn to give them time to get through the multitude. Even then, the bishops in their purple-fringed robes were forced to abandon their bus when it bogged down in the crowd.
By the time the Mass was supposed to start, the multitude had become a "megatude."
"These are the greatest numbers I have ever seen," said Archbishop John P. Foley, a Vatican official from the United States. He said that even the record-setting 2 million who turned out to see the pope in Krakow, in his native Poland, a year after his 1978 election, was a small crowd by comparison.
"This is an excess of success," said the papal spokesman, Joaquin Navarro-Valls. The pope, he said, was "delighted."
"It is his first trip for such a long time, and he has found this kind of reception," Mr. Navarro-Valls said.
The pope himself reached the altar 80 minutes late. Resplendent in gold robes, he was helped by an aide to clamber from a helicopter and onto the altar. He seemed struck by the size of the throng before him, his lips quivering as if in silent prayer.
The pope left Rome on Wednesday to begin an 11-day trip through the Philippines, Papua New Guinea, Australia and Sri Lanka -- his longest journey in three years and the first since a broken leg and slow convalescence forced him to cancel visits to Belgium and the United States last year.
The high point of the pilgrimage was the Youth Day celebration, an occasion the pope himself created 10 years ago to tap into what he sees as the great reservoir of faith and uncynical belief among young people. The international celebrations are held on alternate years.
As in Denver, the young people chanted, "John Paul II, we love you," and in return he ad-libbed small confessions, saying that he, too, had been impatient with the old folk when he was a young man. He made wry faces, and people laughed, and he told them they were "very good people -- incredible but true."
And, as in Colorado, he seemed to take the sight of so many young followers as an opportunity both to recharge himself emotionally and physically, and to exhort them not to follow others into what he called the "moral slavery" of sexual permissiveness and alcohol and narcotics abuse.
"How many young people think they are free because they have thrown off every restraint and every principle of responsibility?" the pope said. "They abuse the beautiful gift of sexuality; they abuse drink and drugs, thinking that such behavior is all right because certain sectors of society tolerate it.
"Millions of young people the world over are falling into subtle but real forms of moral slavery," he said.
At the same time, though, he told the young worshipers -- who came from countries around the world, including the United States -- that they were the hope of the future.
"For on you will depend the Third Millennium, which sometimes appears as a marvelous new epoch for humanity but which also raises not a few fears and anxieties," he said.
The huge enthusiasm for the Mass largely eclipsed the diplomatic thrust of the pope's visit to Asia, the least Christianized of the world's continents. Less than 3 percent of Asians are Roman Catholics -- the bulk of them in the predominantly Catholic Philippines.
The central issue is China, where the Vatican is seeking an acknowledgment of papal authority from the state-controlled Catholic Patriotic Association in return for the Vatican's full recognition that they are Catholics. China insists that the Vatican withdraw its recognition of Taiwan before it will agree to diplomatic relations.