Pope Benedict XVI told America's Roman Catholic leaders Wednesday evening that the clergy sex abuse scandal has sometimes been "very badly handled" by the church.

Benedict made his comments during a prayer service with hundreds of U.S. bishops at the Basilica of the National Shrine of the Immaculate Conception in Washington, D.C.

He said that bishops have spoken with him of the "enormous pain" caused in their communities by the scandal and that "loving concern" would continue to be shown to the victims of the abuse.

The comments mark the second time the pope has addressed sex abuse on his journey to the U.S., and they are the harshest criticism yet of the bishops themselves.

On his flight to America, the pope said he was deeply ashamed of the scandal and would fight to keep pedophiles out of the priesthood.

On Wednesday, he also raised concerns that America society at large has become too sexualized, with pornography and violence easily viewed in many homes.

He also urged America to continue welcoming immigrants to the country, saying that Catholic leaders around the world have been supportive of immigrants for a long time.

"From the beginning they have welcomed the tired, the poor, the huddled masses yearning to breathe free," Benedict said, evoking the words inscribed on the base of the Statue of Liberty. "These type of people are those who Americans have made their own."

Pope Gets Birthday Welcome

The service marked the end of a heady day for Benedict, who drew an enthralled crowd of 13,500 people to a South Lawn arrival ceremony at the White House earlier in the day. The event turned into an 81st birthday party for the pontiff, complete with singing and a cake prepared by the White House pastry chef. Watch the crowd sing here.

"We need your message to reject this dictatorship of relativism and embrace a culture of justice and truth," Bush said in brief remarks welcoming Benedict to the White House. "In a world where some see freedom as simply the right to do as they wish, we need your message that true liberty requires us to live our freedom not just for ourselves, but in a spirit of mutual support."

Benedict thanked Bush and the American people for the warm welcome he received.

"I trust that my presence will be a source of renewal and hope for the church in the United States and strengthens the resolve of Catholics to contribute even more responsibly to the life of this nation of which they are proud to be citizens," the pope said.

The White House threw an elaborate ceremony for the pope, complete with the American and Vatican anthems and a 21-gun salute.

Bush told Benedict that millions of people in this country have prayed for his visit, and that the U.S. is a nation of prayer that welcomes the faithful.

As he left the White House, thousands of screaming fans lined Pennsylvania Avenue as police escorted him in the popemobile to the Vatican Embassy.

During his flight to the United States on Tuesday, the pontiff told reporters he would like to speak with Bush about reform of U.S. immigration laws. Human rights and religious tolerance are also high on his agenda.

Meanwhile, unease with the pope's approach to Islam has led a U.S. Muslim group to decline joining in an interfaith event with him Thursday evening.

Other U.S. Muslim leaders expressed similar concerns about the pope but have pledged to participate in the Washington, D.C., gathering, saying the two faiths should do everything possible to improve relations.

Muslim, Jewish, Buddhist, Jain and Hindu leaders are to take part in the meeting.

But Salam al-Marayati, executive director of the Muslim Public Affairs Council, said the event seemed "more ceremonial than substantive" and that his organization won't participate.

The pope has been praised by supporters for his frankness in approaching Islam and interfaith dialogue in general, but critics have called him insensitive.