NEW YORK — Growing up, Mayor Bill de Blasio was the only child on his block who did not attend Mass on Sundays. “Everyone else was at church, and I wasn’t,” he recalled in an interview last week. “Some of the kids envied me.”

His mother, a lapsed Catholic, had little interest in organized religion, and de Blasio inherited her skepticism. To this day, he belongs to no church and prefers to call himself “spiritual” rather than religious.

Yet as the leader of a famously secular city, de Blasio has been emerging as something unexpected: a champion of religion whose administration has advanced the cause of faith groups in the unlikeliest of public squares.

In de Blasio’s New York:

  • Public pre-kindergarten classes will soon be able to include a midday break for observant students to pray.
  • Schools will be closed citywide for two Muslim holy days.
  • He is poised to relax health regulations governing a controversial circumcision ritual that is favored by some ultra-Orthodox Jews.
  • And the mayor says he is intent on finding a way for church groups to continue holding services in public schools on weekends, even as the US Supreme Court considers taking up a case as early as next week on whether the city has the right to prohibit the practice.

In finding novel ways to commingle church and state, de Blasio, a Democrat, has carved himself a niche as a more inclusive kind of liberal, one who is willing to embrace religious groups rather than treat them as adversaries.

His moves have put him at odds with some of his usual allies, like civil libertarians, who are increasingly uneasy with what they consider to be an aggressive redefining of the proper separation between the secular and the devout.

“This is the area that has been the source of greatest disappointment for us,” said Donna Lieberman, the executive director of the New York Civil Liberties Union.

Many of de Blasio’s religious initiatives began as campaign promises, made during his courtship of evangelicals, Muslims, Orthodox Jews, and other religious groups that now make up a substantial portion of the city. They are groups that often felt frustrated by the administration of Michael Bloomberg, a political independent who was avowedly secular and insisted on a strict church-state divide.

“The progressive political community, of which de Blasio considers himself a part, tends to have a more secularist view of the world, and you would not describe us as a progressive community,” said Rabbi David Zwiebel, executive director of Agudath Israel of America, an umbrella organization for ultra-Orthodox Jews. “We will holler about same-sex marriage and all the rest.”

“But when you get down to the level of actual governance,” Zwiebel added, “down to efforts to try to respect the community’s sensitivities and religious traditions, my own view is that we have a real friend in City Hall.”

In an interview last week, de Blasio described religious outreach as inseparable from his work to create a more inclusive and equitable New York.

“If you are going to understand the community and the city, you have to understand how deeply faithful people are and how central it is to people in their lives,” he said.

De Blasio had an Italian great-uncle, Alberto , who was a priest, but he died when the mayor was young. His mother drifted from the church in her 20s, and religion “was not a particular focal point” for his father, the mayor recalled. De Blasio’s wife, Chirlane McCray, grew up in an Episcopal home, attending Sunday school and church camps, but stopped practicing in college.

“I don’t think she felt the pertinence in her life,” de Blasio said.

Today, the family does not attend church, but the de Blasio children, Chiara and Dante, were camp counselors at Beth Elohim, a Jewish Reform congregation in Brooklyn.

Despite his lack of personal religious observance, de Blasio has long seen faith groups as engines of social change. As a student at New York University, he became immersed in liberation theology, a movement within the Roman Catholic Church that focuses on social justice, and he began his career as an organizer by working with liberal Catholic groups in Nicaragua.

As mayor, he has struck a strong bond with Cardinal Timothy Dolan, leader of the Roman Catholic Archdiocese of New York. Catholic officials have commented on a “different tone” under de Blasio, compared with his predecessor, even though de Blasio boycotted the St. Patrick’s Day parade on Tuesday for its failure to include more gay groups. Dolan was the parade’s grand marshal.

De Blasio said he had sought pragmatic ways to work with faith groups, to ensure that his social programs could reach the greatest number of New Yorkers. For instance, when City Hall started its expansion of free, full-day pre-kindergarten classes last year, the mayor’s team looked to religious schools to host some of the programs, even though they were to be financed with taxpayer dollars and were required to be open to nonreligious students as well.

Some Orthodox Jewish groups agreed, although with some demands — including the option of including a midday break for religious students to pray. To assuage concerns that students might feel coerced to worship, mayoral aides promised to vigorously respond to any complaints. But critics said 4- and 5-year-olds would not necessarily come forward.

“The administration’s efforts to accommodate religious providers has morphed into promoting religion, in a way that breaches the constitutional divide,” Lieberman, of the civil liberties organization, said.

De Blasio, in the interview last week, said he viewed the break as an “artful, respectful solution” that addressed the concerns of religious groups, but kept the formal school day separate from students’ prayer.

“I understand the role of civil libertarians,” the mayor said. But he added, “When it comes to the notion of public policy and what we are trying to achieve through public policy, I am going to be creative, in a very appropriate way, to get that done.”

The mayor’s big-tent approach was apparent this month, when he announced the addition of two Muslim holidays to the city’s public school calendar. Muslim activists called it a watershed moment. The mayor said his decision was a simple “matter of fairness.”

It could become a legal matter, as well. Some lawyers say a secular reason is needed to justify a school closing, for instance, a critical mass of instructors or students who might be absent.

David Bloomfield, a former general counsel for the New York City Board of Education, said the mayor’s move amounted to an unconstitutional endorsement of one religion over another for political gain. By the same logic, Bloomfield asked, why not close schools on Hindu and Buddhist holidays as well?

“He’s marginalized certain cultures and religions by pandering to others,” Bloomfield said. “Bill de Blasio thinks of religious groups like any other constituency, and his problem is that the Constitution doesn’t treat religion as just another constituency.”

Maya Wiley, the mayor’s counsel, was asked in an interview if the Muslim school holidays could be challenged for lacking a sufficient secular purpose.

“Like the secular purpose we have at Christmas?” Wiley replied. “Like the secular reason we have at Easter?” She described the school closings as an appropriate recognition of a religious group that is quickly growing in New York. “I feel very comfortable we’re on the right side,” she added.

De Blasio could soon face a fresh challenge on this front. The Supreme Court could announce as early as Monday whether it will hear a First Amendment case, originally filed two decades ago, involving a small evangelical congregation in the Bronx that was denied the right to rent a public school building for worship on Sundays.

A city Education Department regulation has long barred religious organizations from using school buildings for worship services, but the practice has been permitted since 2002 under a series of legal rulings. The Bloomberg administration vigorously pressed for the ban to be upheld in court, and a federal appeals court has twice sided with the city. Churches, however, were allowed to continue using the buildings, pending the outcome of the legal case.

As public advocate, de Blasio marched across the Brooklyn Bridge with faith groups calling for the prohibition to be lifted. After he became mayor, the city’s Law Department confused evangelical leaders when it elected to move ahead with the case and later filed a brief with the Supreme Court arguing that the city’s ban on worship services in schools is constitutional. (City Hall officials say they are trying to preserve their prerogative to regulate use of public school facilities for all groups, including faith groups.) But de Blasio reiterated in the interview his support for the right for churches to use the buildings.

“My interpretation of the Constitution is it protects the right of people to have any faith, or no faith,” the mayor said.

A boys’ club, youth league, or a religious group, the mayor said, “should have the equal right to rent the space for the same price.”