WASHINGTON (CNS) -- The pope warned of "signs of a disturbing breakdown in the very foundations of society" and said people need the church's message of hope and fidelity to the demands of the Gospel.

He also confronted the question of clerical sexual abuse of minors, acknowledging the damage done to the church and asking all Catholics to help assist those who have been hurt.

The Mass April 17 at a packed Nationals Park was the pope's first major encounter with the Catholic faithful on his six-day visit to Washington and New York.

The liturgy, celebrated on an altar platform in deep center field, was a Mass of the Holy Spirit and featured multiethnic choirs singing in four languages.

The spirit was evident among the enthusiastic crowd of about 45,000 people, who cheered the 81-year-old pope as he rode through the stadium in his popemobile.

The pope smiled, waved and looked delighted at the panorama of faces and fluttering yellow flags, as the choirs sang English and German versions of "Holy God, We Praise Thy Name."

Anne Murphy, a member of Blessed Sacrament Parish in Alexandria, Va., remarked on the "spirit of togetherness" the pope's presence had brought.

"I think it's a very exciting opportunity for people throughout the country to witness the kind of spiritual power that (Pope) Benedict brings to the world," she said.

"It's the kind of thing that makes you proud to be a member of the Catholic community and to be here today," she said.

After the pope processed to the altar, he was welcomed by Washington Archbishop Donald W. Wuerl, who told him U.S. Catholics looked to him for "renewed inspiration to continue the challenge to make all things new in Christ our hope."

The pope, dressed in red vestments, opened his arms wide in appreciation.

In his homily, the pope said he had come to encourage the church in America to build on its accomplishments and respond to new challenges through an "unceasing missionary outreach."

He invoked a new chapter of the descent of the Holy Spirit at Pentecost, saying U.S. Catholics need to give their contemporaries "a convincing account of the hope which inspires them."

"The world needs this witness. Who can deny that the present moment is a crossroads, not only for the church in America but also for society as a whole?" he said.

The pope said that it was a positive thing that global connections were drawing people together today.

"Yet at the same time we see clear signs of a disturbing breakdown in the very foundations of society: signs of alienation, anger and polarization 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," he said.

This crossroads is also reflected inside the church, he said. He cited the vitality of movements and parish life and increased interest in prayer and Catholic education.

Yet the church faces the "troubling realization" that many of its members, "rather than acting as a spiritual leaven in the world, are inclined to embrace attitudes contrary to the truth of the Gospel."

Today's challenges require sound instruction in the faith, especially among the young, he said. But they also call for "cultivating a mindset, an intellectual culture, which is genuinely Catholic" and can bring the Gospel to bear on the urgent issues American society faces, he said.

The pope spoke about sexual abuse by priests for the third time in three days. The evening before, he addressed the bishops; this time, he aimed his comments at the entire U.S. Catholic community. He also spoke about it to journalists on the papal plane from Rome April 15.

"No words of mine could describe the pain and harm inflicted by such abuse. It is important that those who have suffered be given loving pastoral attention," he said.

He lauded the efforts to deal "honestly and fairly with this tragic situation, and to ensure that children -- whom Our Lord loves so deeply and who are our greatest treasure -- can grow up in a safe environment."

"I encourage each of you to do what you can to foster healing and reconciliation and to assist those who have been hurt. Also, I ask you to love your priests and to affirm them in the excellent work that they do," he said.

The pope said the church's ability to heal wounds and overcome divisions depends in part on the rediscovery of the "liberating power" of the sacrament of penance.

That will help the church in the United States become a "leaven of hope" in society, and take its place in the long story of the church's expansion, he said.

The pope spoke about the past injustices endured by native Americans and by Africans brought forcibly to the country as slaves. But essentially, he said, Americans have always been a people of hope and open to the Christian message.

At the end of his homily, the pope spoke in Spanish, thanking the increasing number of Hispanic Catholics for adding vitality to the church in the United States.