VATICAN CITY —  Pope John Paul II (search) warned several U.S. bishops Friday that American society is in danger of turning against spirituality in favor of materialistic desires, giving way to a "soulless vision of life."

To fight this, the pontiff argued, the U.S. church must study contemporary culture to find a way to appeal to youths. He made his remarks to bishops from Indianapolis, Chicago and Milwaukee who were making a periodic visit to the Vatican.

The American church "is called to respond to the profound religious needs and aspirations of a society increasingly in danger of forgetting its spiritual roots and yielding to a purely materialistic and soulless vision of the world," John Paul said.

"Taking up this challenge, however, will require a realistic and comprehensive reading of the 'signs of the times,' in order to develop a persuasive presentation of the Catholic faith and prepare young people especially to dialogue with their contemporaries about the Christian message and its relevance to the building of a more just, humane and peaceful world."

John Paul added: "An effective proclamation of the Gospel in contemporary Western society will need to confront directly the widespread spirit of agnosticism and relativism which has cast doubt on reason's ability to know the truth, which alone satisfies the human heart's restless quest for meaning."

All bishops must visit the Vatican every five years. This year is the Americans' turn, and several regional delegations already have met with the pope.