The Pope today used an extraordinary Mass in front of 46,000 people at a baseball stadium to criticise a lack of equality and an increase in violence in American society.

Wearing scarlet vestments, Benedict XVI led the service from a special altar in the middle of the recently inaugurated Nationals Park in Washington.

In his sermon the Pope said hope "is very much a part of the American character" - but said all not all ethnic groups would agree.

"Americans have always been a people of hope," he said. "Your ancestors came to this country with the experience of finding new freedom and opportunity.

"To be sure, this promise was not experienced by all the inhabitants of this land; one thinks of the injustices endured by the native American peoples and by those brought here forcibly from Africa as slaves."

He went on to lament "clear signs of a disturbing breakdown in the very foundations of society: signs of alienation, anger and polarisation on the part of many of our contemporaries; increased violence; a weakening of the moral sense; a coarsening of social relations and a growing forgetfulness of God."

The Pope then turned for a third day to the clergy sex abuse scandal that rocked the American Church and has cost US dioceses $2 billion in damages.

"No words of mine can describe the pain and harm inflicted by such abuse," he said.

"It is important that those who have suffered be given loving pastoral attention. Nor can I adequately describe the damage that has occurred within the community of the Church."

Bill Fay, a Catholic from Rockville, Maryland who attended the Mass, said the scandal had not shaken his faith and that he decided to keep his children in Catholic schools.

However, he was critical of the way the Church handled the crisis. "They did a fairly good job of attempting to sweep it under the rug," he said.

Later today the pontiff, who turned 81 yesterday and was feted at the White House, will address heads of Catholic universities and schools and meet leaders of other religions. He goes to New York tomorrow to address the United Nations and returns to Rome on Sunday after visiting the site of the former World Trade Centre.