PARIS?Pope Benedict XVI Friday threw his weight behind a call by President Nicolas Sarkozy to rethink the strict separation of religion and state in France, the "eldest daughter" of the Catholic Church.

Bells tolled across Paris to greet the arrival of the leader of the world's one billion Roman Catholics, whose four-day visit comes as France faces a freefall in the number of churchgoers despite its deep Christian heritage.

President Nicolas Sarkozy and his wife Carla Bruni travelled to greet the 81-year-old pontiff at Orly airport and escort him to the Elysee palace for a reception with dozens of political and religious leaders.

Sarkozy, who broke a taboo during a trip to the Vatican last year by calling for a "positive secularism" allowing space for religion in public life, made a point of welcoming the pope to Paris in the name of the "secular republic of France."

Speaking in fluent French, the pope replied that it was "fundamental" to "insist on the distinction between the political realm and that of religion" but also to recognize the role of religion in building an "ethical" society, according to the official Vatican English text of his speech.

"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 'laicite' (secularism) is now necessary," the pope said.

While Catholicism remains by far France's number one religion, the country is also home to Europe's biggest Muslim and Jewish communities and staunchly upholds a 1905 law that enshrines the separation of Church and State.

Several groups here -- mostly unions and leftists -- are planning protests against Sarkozy's call for religion to be more than a strictly private affair.

France's opposition Socialist Party put out a statement on Friday urging Sarkozy to uphold French "secular principles."

But Sarkozy, a twice-divorced lapsed Catholic, defended his vision in presence of the pope, saying it would be "madness" to "deprive ourselves" of religion.

"We don't put anyone above anyone else, but we accept our Christian roots," Sarkozy said. "That does not stop us from doing everything to ensure our Muslim compatriots can live their faith equally with all others."

Benedict was later to meet French Jewish leaders as they prepared to observe the Sabbath, before delivering a keynote address to some 700 cultural and religious leaders including from France's five-million strong Muslim community.

After leading an open-air mass in central Paris Saturday, the pope flies to Lourdes for commemorations of the 150th anniversary of the Vatican-recognized apparitions of the Virgin Mary to a peasant girl.

More than 200,000 people are expected to descend on the southwestern town where Bernadette Soubirous is said to have seen the mother of Jesus Christ 18 times over a period of a few months in 1858.

This is Benedict's first trip to France since his election in 2005 following the death of John Paul II and his 10th trip abroad after Australia in July.

Known as the Church's "eldest daughter" since Frankish king Clovis converted in the fifth century, France is home to 35 million baptized Catholics, although polls show few feel a strong sense of belonging to the Church.

A survey published last year showed 51 percent of the French consider themselves Catholic, down from 80 percent in the early 1990s.

Of those, only 10 percent attend mass regularly, the survey in Le Monde des Religions magazine showed.

The pope wraps up his trip Monday with a mass for the sick in Lourdes -- which also has a reputation for miraculous cures -- that the Vatican has portrayed as an opportunity for Benedict to shed his reputation as a cold theologian and show his compassionate side.

Some 9,200 police will be mobilized to ensure security during the visit.