VATICAN CITY — Pope Benedict XVI accepted the resignation of Philadelphia archbishop Cardinal Justin Rigali on Tuesday, sending him into retirement as the archdiocese faces accusations that it covered up a long-running priest sex abuse scandal.

The pope named conservative Denver Archbishop Charles Chaput to succeed him.

The brief Vatican announcement said the resignation of the 76-year-old Rigali was for reason of age. He submitted it on his 75th birthday in April 2010, as required by church law, but the pope did not immediately act on it.

But the Cardinal has been under pressure for his handling of the sex-abuse scandal. In his eight-year tenure, a pair of grand jury reports, one in 2005 and one released in February, have rocked the archdiocese by accusing church officials of covering up abuse allegations against priests.

February's scathing report resulted in unprecedented criminal charges against a former secretary of clergy for allegedly transferring pedophile priests without warning new parishes.

The grand jury accused church officials of keeping 37 clergy in active ministry despite credible claims that they had sexually abused young people. The allegations came nine years after U.S. bishops promised at the height of the clergy abuse crisis to oust all predators from ministry.

A onetime archdiocesan administrator in Philadelphia, Monsignor William Lynn, was charged with child endangerment for allegedly leaving the accused clerics in church jobs without warning parents or police. Lynn, the highest-ranking U.S. church official criminally charged with sheltering abusers, says he is innocent. Two other priests and a former priest are also charged.

Rigali responded to the report by suspending 23 priests and hired two former city prosecutors to review abuse cases. Ana Maria Catanzaro, head of the local Philadelphia review board, which helps the archdiocese evaluate abuse claims, said Philadelphia church officials had kept some cases from the panel and had "failed miserably at being open and transparent."

Victim advocates claimed that Rigali delegated much of the responsibility for child protection to others and offered little support to victims. Rigali, who usually shuns publicity, also had to deal with fallout from a 2005 local grand jury report that claimed his predecessors, including immediate predecessor Anthony Bevilacqua, hid abuse by priests for decades and failed to notify authorities of the crimes.

Rigali, a former archbishop of St. Louis, spent three decades as a Vatican diplomat and high-level administrator and has kept his close contacts in Rome. He remains a Cardinal and can vote in the conclave to elect a new pope until his 80th birthday.

The archdiocese scheduled a news conference for 10 a.m. to introduce Chaput, followed by a Mass led by Rigali and attended by the new Archbishop.

Chaput, 66, is known as an outspoken U.S. bishop who has criticized Catholic politicians who support abortion rights, speaks out against government playing too big a role in health care and opposes gay marriage and stem-cell research.

In 2010, he defended a decision by a Catholic school in Colorado not to re-enroll two children of a lesbian couple. Chaput said the parents of Catholic school students are expected to agree with church beliefs, including those forbidding sex between anyone other than married, heterosexual couples.

Chaput was one of the bishops Benedict chose in 2009 to investigate the Legionaries of Christ, the disgraced religious order that in recent years confirmed that its late founder fathered three children and sexually abused young seminarians. The pope also turned to Chaput in another sensitive case: an inquiry into Australian Bishop William Morris of the Toowoomba diocese, who Benedict removed in May partly because the bishop indicated he would ordain women and marry men if church rules allowed the practice.

Between 2005 and 2008, the archdiocese of Denver settled 43 sex abuse allegations against priests for a total of $8.2 million. Chaput has publicly apologized to all the victims, saying the church was "mortified and embarrassed."

"It's obvious Rome is asking Archbishop Chaput to handle several very tough and sensitive jobs," said Russell Shaw, a former spokesman for the U.S. Conference of Catholic Bishops who is friendly with Chaput. "He was regarded in Rome already as a very able and reliable man who could be counted on to do a good honest job and do it well."

In Philadelphia, Rigali has overseen the closing of dozens of Catholic schools because of declining enrollment, but he also spearheaded the construction of two suburban high schools and a church for a burgeoning immigrant Hispanic community.

AP correspondent Alessandra Rizzo contributed from the Vatican.