WASHINGTON (CNN) -- Pope Benedict XVI on Wednesday addressed issues ranging from the sex abuse scandal in the Roman Catholic Church to the easy availability of pornography to the "alarming decrease" in Catholic marriages in the United States.



The pope arrives to address U.S. bishops in the Basilica of the National Shrine of the Immaculate Conception.



He spoke at a prayer service with U.S. bishops at Washington's Basilica of the National Shrine of the Immaculate Conception, the largest Roman Catholic church in North America.



Benedict said the sexual abuse of children by priests has caused a "deep shame" and called it "gravely immoral behavior."



"Many of you have spoken to me of the enormous pain that your communities have suffered when clerics have betrayed ... their obligations," he told the bishops.



Responding to the situation has not been easy and was sometimes very badly handled, the pope admitted.  Watch the pope address the issue »



"It is vitally important that the vulnerable are always shielded from souls who would cause harm," he said.



The pope then turned his attention to a different concern involving kids.



"What does it mean to speak of child protection when pornography and violence can be viewed in so many homes through media widely available today?" he asked.



Benedict urged the media and entertainment industry to take part in a "moral renewal."



Earlier Wednesday, President Bush, first lady Laura Bush and more than 13,500 spectators welcomed Benedict in an elaborate ceremony on the South Lawn of the White House.



In remarks greeting the pope to the White House, Bush called the United States "a nation of prayer."



Bush was interrupted by applause as he said, "In a world where some treat life as something to be debased and discarded, we need your message that all human life is sacred and that each of us is willed."



Benedict responded by praising the role of religion in the United States.



"From the dawn of the republic, America's quest for freedom has been guided by the conviction that the principles governing political and social life are intimately linked to a moral order based on the dominion of God the creator," he said.  Watch Benedict talk about his hopes for the trip »



Earlier, a U.S. Marine Corps band performed the national anthem of the Holy See as well as "The Star-Spangled Banner."



A fife and drum corps in Colonial costumes also played tunes, including "Yankee Doodle," and soprano Kathleen Battle sang "The Lord's Prayer."



The day, with perfect spring weather, was also the pontiff's 81st birthday.  After the ceremony concluded, the crowd, led by Battle, serenaded Benedict with "Happy Birthday" as he smiled from a White House balcony.  Watch a priest who has known Benedict for years tell what he's like »



Guests on the South Lawn included Catholic clergy, ecumenical representatives, Catholic schoolchildren, Boy Scouts, Girl Scouts, Sisters of the Poor and Knights of Columbus.



Event planners faced an enormous demand for tickets for what White House press secretary Dana Perino called "one of the largest arrival ceremonies ever held at the White House."



Following the ceremony, Bush and the pope had a one-on-one meeting in the Oval Office.



The pope left the White House at about noon in his distinctive "popemobile."



His massive motorcade moved slowly down the wide avenues of the U.S. capital to the Vatican Embassy, where the pope is staying. Crowds of enthusiastic spectators waved U.S. and Vatican flags and screamed as the pontiff rode past.



A smiling Benedict arrived Tuesday at Andrews Air Force Base in Maryland to cheers from a crowd of invited guests. The pontiff was greeted by Bush, the first lady and their daughter Jenna, each of whom shook his hand.



It was believed to be the first time an American president has greeted a world dignitary on arrival at Andrews. It marks Benedict's first visit to the United States as pope.   Watch how the pope's visit could affect the presidential campaign »



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What transportation will the pope use? What will he celebrate? Who spoke to bishops about the abuse of children? What did the Pope discuss? When did the pope and president discuss? What was the behavior labelled?
"popemobile." 81st birthday. Pope Benedict XVI issues ranging from the sex abuse scandal Wednesday, "gravely immoral
question: What transportation will the pope use?, answer: "popemobile." | question: What will he celebrate?, answer: 81st birthday. | question: Who spoke to bishops about the abuse of children?, answer: Pope Benedict XVI | question: What did the Pope discuss?, answer: issues ranging from the sex abuse scandal | question: When did the pope and president discuss?, answer: Wednesday, | question: What was the behavior labelled?, answer: "gravely immoral