Several experts on the Catholic Church and Islam agreed that the speech — in which Benedict made clear he was quoting other sources on Islam — did not appear to be a major statement on, or condemnation of, Islam. The chief concern, they said, was the West's exclusion of religion from the realm of reason.

Still, they said that the strong words he used in describing Islam, even that of the 14th century, ran the risk of offense.

Renzo Guolo, a professor of the sociology of religion at the University of Padua, who often writes about the church and Islam, said he was struck by the suggestion of Islam as distant from reason.

"This is maybe the strongest criticism because he doesn't speak of fundamentalist Islam but of Islam generally," he said. "Not all Islam, thank God, is fundamentalist."

The Rev. Daniel A. Madigan, rector of the Institute for the Study of Religions and Cultures at the Pontifical Gregorian University in Rome, said the central point was that "if we are really going into a serious dialogue with Muslims, we need to take faith seriously." But, he said of the quote from the emperor, "You clearly take a risk using an example like that."

Marco Politi, the Vatican expert for the Italian newspaper La Repubblica, said that "the text reveals his deep mistrust regarding the aggressive side of Islam."

"Certainly he closes the door to an idea which was very dear to John Paul II — the idea that Christians, Jews and Muslims have the same God and have to pray together to the same God," he said.

The speech was a central moment in Benedict's six-day trip home to visit Bavaria, where he grew up, became a priest, a prominent theologian and, finally, a cardinal. Earlier in the day, at an outdoor Mass here attended by some 250,000 people, he expressed similar concerns as in the speech, urging believers to stand up against the "hatred and fanaticism" that he said were tarnishing the image of God.

Again, this critique seemed aimed as much at secular Western society as at any other threat.

"Today, when we have learned to recognize the pathologies and life-threatening diseases associated with religion and reason, and the ways that God's image can be destroyed by hatred and fanaticism, it is important to state clearly the God in whom we believe," the pope said.

"Only this can free us from being afraid of God — which is ultimately at the root of modern atheism," he said. "Only this God saves us from being afraid of the world and from anxiety before the emptiness of life."

The speech at the university was the only significant secular event in a schedule packed with Masses, evening prayers and other religious occasions aimed at Catholics in Germany, where regular Mass attendance has plummeted to under 15 percent.