“It is through the search for God that the secular sciences take on their importance.”

His message went counter to a deep vein of anticlericalism in France, which has long drawn sharp distinctions between issues of faith and matters of temporal power.

“At this moment in history, when cultures continue to cross paths more frequently, I am firmly convinced that a new reflection on the true meaning and importance of secularism is now necessary,” the pope said at a ceremony earlier Friday with President Nicolas Sarkozy at the Élysée Palace. He used the word “laïcité,” which denotes the separation of church and state.

But the pope proposed a “distinction between the political realm and that of religion in order to preserve both the religious freedom of citizens and the responsibility of the state toward them.” He distinguished the state’s legislative and social duties from religion’s role “for the formation of conscience” and the “creation of a basic ethical consensus in society.”

Image Pope Benedict XVI waving at crowds on Friday outside the Cathedral of Notre-Dame during his first visit to France as pope. Credit... Thibault Camus/Associated Press

After his speeches, the pope said a Mass for young people at the Cathedral of Notre-Dame.

The pope’s four-day stay in France had been planned to commemorate the 150th anniversary of what the Vatican recognizes as the apparitions of the Virgin Mary to a 14-year-old peasant girl, Bernadette Soubirous, at Lourdes in 1858. He broadened his journey at the invitation of Mr. Sarkozy, who spoke during a visit to Rome and the Vatican last year of a “positive secularism,” saying religion “should not be considered a danger but an asset.”