The return of indulgences began with Pope John Paul II, who authorized bishops to offer them in 2000 as part of the celebration of the church’s third millennium. But the offers have increased markedly under his successor, Pope Benedict, who has made plenary indulgences part of church anniversary celebrations nine times in the last three years. The current offer is tied to the yearlong celebration of St. Paul, which continues through June.

Dioceses in the United States have responded with varying degrees of enthusiasm. This year’s offer has been energetically promoted in places like Washington, Pittsburgh, Portland, Ore., and Tulsa, Okla. It appeared prominently on the Web site of the Diocese of Brooklyn, which announced that any Catholic could receive an indulgence at any of six churches on any day, or at dozens more on specific days, by fulfilling the basic requirements: going to confession, receiving holy communion, saying a prayer for the pope and achieving “complete detachment from any inclination to sin.”

But in the adjacent Archdiocese of New York, indulgences are available at only one church, and the archdiocesan Web site makes no mention of them. (Cardinal Edward M. Egan “encourages all people to receive the blessings of indulgences,” said his spokesman, Joseph Zwilling, who said he was unaware that the offer was not on the Web site, but would soon have it posted.)

The indulgences, experts said, tend to be advertised more openly in dioceses where the bishop is more traditionalist, or in places with fewer tensions between liberal and conservative Catholics.

“In our diocese, folks are just glad for any opportunity to do something Catholic,” said Mary Woodward, director of evangelization for the Diocese of Jackson, Miss., where only 3 percent of the population is Catholic.

Even some priests admit that the rules are hard to grasp.

“It’s not that easy to explain to people who have never heard of it,” said the Rev. Gilbert Martinez, pastor of St. Paul the Apostle Church in Manhattan, the designated site in the New York Archdiocese for obtaining indulgences. “But it was interesting: I had a number of people come in and say, ‘Father, I haven’t been to confession in 20 years, but this’ ”  the availability of an indulgence  “ ‘made me think maybe it wasn’t too late.’ ”