Stephen Um is the Korean-born pastor of the Citylife Church in Boston, a 10-year-old Presbyterian Church in America (PCA) congregation that meets in a hotel and attracts 800 weekly attendees. He ministers to Boston’s youthful and professional elite: 35 percent of his half-white, half-Asian congregation has at least one postgraduate degree.

But his ministry focuses on empowering individuals to bear witness, challenge atheist assumptions, and do good works – not change public policy for Christ.

On a snowy 20-degree day in December, the visitors shiver as they move among vestiges of a long-closed Pizza Hut on this city’s struggling main street. A salad bar teeters off kilter. Dust collects on the dismantled facade of a soda dispenser. A few bolted-down tables and chairs remain – usable, but only after a good cleaning.

Yet none of this bothers the three leaders from the Auburn Seventh-day Adventist Church, who seem warmed by holy fire to carry out their task: Help transform the pizza joint into something with a bit more piety. Their church has reached capacity, having doubled attendance in the past year. So they’ve crossed the Androscoggin River to plant a second church, the Ark, in the heart of one of the nation’s least religious states.

This won’t be worship as usual. Starting early in the new year, a smorgasbord of community services will be served where deep-dish pepperoni used to be the lure. Vegetarian cooking classes and health seminars, hydrotherapy treatments and massage instruction, marriage classes and smoking-cessation clinics – all will be free of charge and led by volunteers. A vegan restaurant will open to bring in revenue. Worship services will begin next spring.

“It’s almost like you have to use a place like a Pizza Hut,” says Tracy Vis, a new member of the Auburn church. “Some people are not going to be comfortable with [traditional church buildings] or traditions. But they’ll come here and listen to these different messages.”

The Ark is symbolic of a transforming religious landscape in New England. Long defined by dominant Roman Catholic and mainline Protestant institutions, the terrain is undergoing a fundamental shift as traditional denominations cope with steep declines in membership and shutter churches and seminaries.

At the same time, evangelical and Pentecostal groups are doing just the opposite. They’re expanding their footprint in what statistics show are America’s four least religious states: Vermont, New Hampshire, Maine, and Massachusetts. And because more and more Americans today identify with no particular religion, what happens in this land of spiritual free agency could offer insights into the future of religion across the country. The recent changes in New England have been significant:

•Between 2000 and 2010, the Catholic church has lost 28 percent of its members in New Hampshire and 33 percent in Maine. It has closed at least 69 parishes (25 percent) in greater Boston.

•Over the same period, the Southern Baptist Convention (SBC) established 118 new churches in northern New England, according to the 2010 Religion Census. About 50 of them inhabit buildings once owned by mainline churches.

•Other denominations are growing, too, including Pentecostals: Assemblies of God (11 new churches in Massachusetts) and International Church of the Foursquare Gospel (13 new churches in Massachusetts and Maine). The Seventh-day Adventists, an evangelical group, opened 55 new churches in Massachusetts, New Hampshire, and Maine between 2000 and 2010, according to the Religion Census. Muslims and Mormons are experiencing membership gains as well.

More change looms on the horizon. In 2013, northern New England will lose its only mainline Protestant seminary and accredited graduate school of religion when the Bangor Theological Seminary closes in May. Three months later, Southern Baptists will open Northeastern Baptist College – the first SBC-affiliated pastor-training college in northern New England – in Bennington, Vt.

“The old establishment is crumbling in the sense that fewer people are going to church and buildings are being sold off,” says Todd Johnson, director of the Center for the Study of Global Christianity at Gordon-Conwell Theological Seminary in South Hamilton, Mass. “The old expectations aren’t there anymore, and that creates an openness to new brands.”

New England’s changing religious character comes as religious ties decline around the country. Nearly 1 in 5 Americans (19.6 percent) now says he or she has no religious affiliation, up from 15 percent just five years ago, according to Pew Research Center surveys.

Faith remains strong: More than 90 percent of Americans still believe in God or a universal spirit, according to Gallup research, even as fewer claim a particular religious “brand” or identity. More people are opting not to align themselves with one religious denomination or tradition, but their interest in faith remains keen and creates opportunities for innovators.

“The way people are religious is changing,” says Frank Newport, Gallup’s editor in chief. “And maybe what’s happening up in [New England] is a good indication of what is happening or could happen elsewhere.”

Now emerging in the land of Cotton Mather and Robert Frost are religious cultures marked by immigrant experiences and creative worship, with emphasis on good works and personal holiness. It’s not entirely what stolid New Englanders are used to, but maybe that’s its appeal.

* * *

On a December morning, the polished sounds of bongos and electric keyboards emanate from Congregación León de Judá, a 1,500 member church in an ethnically diverse Boston neighborhood. It’s a mainline American Baptist Churches congregation, though maybe not one prior generations would recognize.

The 36,000-square-foot complex looks more suited for offices than offerings, but on this day, 500 pack the sanctuary for an upbeat, bilingual service. A high-stepping man leads a praise chorus. Laypeople take turns praying: one in Spanish, then another in English. Dozens approach the stage for prayer. Hands rise and eyelids fall. After an hour, some 75 English speakers representing 15 countries head downstairs to continue worship in their language.

Another 15 go to a window-filled room where a new Anglican Church in North America congregation, started by León de Judá, is gathering for the first time. Ministries here are growing so fast – 500 new members in the past five years – that a 40,000-square-foot building is rising next door to help house it all.

For new members like Ted Best, who emigrated from Barbados 30 years ago, and William Leslie from Dominica (both English-speaking countries), the church’s Hispanic roots were no barrier. They like being part of a dynamic congregation that provides outlets for compassion and immigrants’ hopes.

“We want to be part of a church that is growing,” says Mr. Leslie, who does outreach work for León de Judá, from visiting hospitals to sharing information in subways. “We want to touch the community for Jesus, and this church has advanced that cause.”

. Researchers at the Emmanuel Gospel Center (EGC), a Boston-based Christian organization that studies urban ministries, call it a “quiet revival.” It is often overlooked because the Religion Census tracks only denominations, yet nondenominational churches account for some of the fastest-filling pews, or folding chairs, as the case may more often be.

EGC data show that Boston has spawned more than 100 Hispanic evangelical churches in the past 40 years, up from just a handful in the 1970s. EGC’s census also found 65 Haitian churches in greater Boston, including at least one with more than 500 members.

“A storefront church might not look that big, but they have 100 to 200 people coming each week,” says Rudy Mitchell, a senior researcher at EGC. “A big old church might only have 50 people attending even though they have a big building.”

Where growth is happening inside traditional denominations, such as at León de Judá, immigrant connections often play a central role. Half of the Southern Baptists’ 325 churches in New England are non-English speaking. They worship instead in Spanish, Portuguese, or Haitian Creole.