VATICAN CITY – Cardinal Bernard Law, whose failures to stop sexually abusive priests sparked the worst crisis in American church history, led a Mass for thousands mourning Pope John Paul II at St. Peter’s Basilica yesterday after police whisked away a victim protesting outside.

Cardinal Law celebrated the Mass without disruption, saying in his homily that Italian, Polish, and other pilgrims were inspiring in their huge tribute to John Paul. Nearly 3 million mourners flooded Rome for the pontiff’s funeral last week.

“In these incredible days, the pope continues to teach us what it means … to be a follower of Christ,” Cardinal Law said, reading slowly in Italian. “Our faith has been reinforced.”

After the service, several worshippers from Europe said they had never heard of Cardinal Law. American parishioners said they recognized him, but questioned whether the protest was appropriate right after the pope died.

“It’s not the time or the place,” said Mary Beth Bauer, who lives in Maine and had followed the abuse crisis and Cardinal Law’s resignation.

But some Catholics said seeing the cardinal presiding over Mass at one of the most significant sites for their faith was another sign that the Vatican did not understand the betrayal parishioners felt for his protecting guilty priests.

The founder of the Survivors Network of those Abused by Priests, Barbara Blaine, and another leader of the advocacy group, Barbara Dorris, said the Vatican’s choice of Cardinal Law devastated victims.

“We believe he should take a back seat and stay in the background so Catholics can grieve without having to have the sex abuse scandal in their face,” said Ms. Blaine, who had flown into Rome just hours before the Mass.

At St. Peter’s Square, Ms. Blaine planned to distribute fliers, but was quickly surrounded by Italian officers who moved her without incident outside the plaza. Ms. Blaine said she felt compelled to travel to the Vatican from her home in Chicago after learning of Cardinal Law’s public role in memorializing the pope. The Mass is one of nine daily services for the pope for the period of mourning called Novemdiales.

Cardinal Law resigned as archbishop of Boston in December 2002 after unsealed court records revealed he had moved predatory clergy among parishes for years without telling parents their children were at risk. He has apologized for his wrongdoing.

More than 550 people have filed abuse claims in Boston in recent years, and the archdiocese has paid more than $85 million in settlements. The scandal erupted in Boston in January 2002 and spread nationwide, causing what American Catholic bishops have called the worst crisis in the American church.

After Cardinal Law’s resignation, the pope appointed him archpriest of St. Mary Major Basilica in Rome, one of four basilicas under direct Vatican jurisdiction. Some church leaders have said the Vatican chose Cardinal Law to celebrate the Mass because he leads an important church, not as a personal honor.