VATICAN CITY (Reuters) - Roman Catholicism faces a serious challenge from the rising number of people who believe in God but no longer see any need for a church, according to New York Cardinal Timothy Dolan.

Cardinal Timothy Dolan, the Archbishop of New York, looks at the helicopter (not pictured) carrying Pope Benedict XVI fly off from the Vatican, on its way to the papal summer residence at Castelgandolfo, February 28, 2013. REUTERS/Yara Nardi

Opinion research shows that some people today have problems "with the very nature and meaning of the church", Dolan, in Rome to prepare for a conclave to elect a replacement to the retired Pope Benedict, told Reuters in an interview.

Dolan said this trend, which sociologists of religion call "believing without belonging", should be high on the list of issues that cardinals discuss at the Vatican next week before they retreat into the Sistine Chapel to vote for the pope.

Benedict officially stepped down on Thursday, the first pope in almost six centuries to do so, and the 115 cardinals due to pick his successor began informal meetings on Friday to discuss procedures for the vote and size up candidates.

"We hear that more and more people have absolutely no problem with faith, but they do with religion," Dolan, 63 and mentioned among possible candidates for the papacy, said.

"While more and more people have no problem at all with Jesus Christ, they love him and accept him as their Lord and saviour, they do have problems with the church," he said. "More and more people don't see the need for the church."

The phrase "believing without belonging", coined by British sociologist Grace Davie in the 1990s, describes the growing number of people who say they are "spiritual but not religious" and leave organised religion behind.

The trend, seen in Europe and North America, has especially hurt established Christian churches that have seen their ranks dwindle.

In the United States, the "nones" - people with no religious affiliation - have grown from seven to 18 percent of the population since 1972, according to a Pew Forum study.

A third of those born after 1980 are unaffiliated, it said, compared to 15 percent among their "baby boom" parents and five percent in their grandparents' generation.

Dolan noted this and other studies showed most Catholics did not abandon the "faith of their fathers", but the church could not ignore the trend. "It is a problem," he said.

For Catholics, he said, faith in and love of Jesus Christ have always been linked with being part of the church.

"The two were a package deal - you don't have one without the other," he said. "We have to reclaim that lustre. We have to reclaim that relationship that Jesus and his church are one."

RELIGIOUS PERSECUTION

The New York archbishop said the Catholic Church, which with 1.2 billion faithful is by far the world's largest church, should also become more active in fighting religious persecution against people of all faiths around the globe.

At a recent synod of bishops to discuss Church efforts to revive Catholicism's missionary spirit, he said, several bishops suggested the Vatican create a separate office to monitor violations of religious liberty around the world.

"If people are persecuted anywhere for their religious belief, they should be able to look to the Catholic Church as a major defender," he said.

Dolan, who has led opposition to the Obama administration's healthcare mandate requiring religious institutions to provide birth control in their health plans, said this office should also monitor violations that "take place not in Third World countries but in First World countries".

"There seems to be a pretty well oiled choreography to reduce religion and faith to the excessively private and where religion may have absolutely no public witness and voice in the public square," he said.

"That's another subtle form of religious persecution."

Reform of the Curia, whose mismanagement has become a pressing issue before the conclave, must be considered but "I don't think we need to get overly obsessed with that," he said.

Dolan has joked that anyone who lists him among potential popes "must have been smoking marijuana", and laughed off talk in Rome that he could emerge from the Sistine Chapel in white papal robes.

"I don't know what other way to say I find that extraordinarily unlikely," he declared.