During a routine evening rehearsal, the choir doesn’t pay attention to its misfit.

A petite woman, slightly right of center in the front row, bears the signs of a choreographed life. The gleaming flaxen bob. The burgundy pantsuit and pearls. An oddity beside singers in denim and Eastman sweatshirts.

The eye might think she does not blend well, but the ear disagrees. When singing Eric Whitacre’s “Lux Aurumque,” a contemporary hymn composed of tight harmonies, Callista Gingrich’s is just one of 26 voices blending to form a ripe sound that rings through the basilica’s apse.

For 15 years, Gingrich, 45, has performed weekly with the choir of the Basilica of the National Shrine of the Immaculate Conception. She and the other choir members are paid, professional singers who can sight-read on command and easlily distinguish Gregorian chant from Renaissance polyphony. She is one of the choir’s most senior members, a steady force in the alto section. Only now is her presence becoming a minor distraction for the congregation, which attends High Mass on Sundays at the Roman Catholic church in Northeast Washington.

“That’s Newt Gingrich’s wife, the bright blonde,” an attendee whispered during their recent annual Christmas concert for charity, where 2,500 listeners recently gathered.

“Reeeaaallly?” A woman reacted as the choir begins to sing a piece by Camille Saint-Saens.

The country’s largest Catholic church may become subject to new distractions, ones that could involve traffic jams and the Secret Service. The choir, too, finds itself in the spotlight, particularly because Newt Gingrich, now the Republican front-runner in Iowa, often praises it when explaining his religious conversion to Catholicism from Southern Baptist.

If Gingrich captures the Republican nomination, he will be the first Catholic-convert nominee on a U.S. presidential ballot. This choir, he says, played a significant role in his spiritual quest.

“It brought me here,” Gingrich said, pointing to the altar after the concert, where he remained in the first pew long after “Joy to the World” ended. “It brought me here to experience the Eucharist and this basilica. It shows that as part of the liturgy, a choir can inspire hearts.”

He pauses, looking up at the altar again. “I had a tear in my eye on the last song, because it reminded me of my mother. My mother sang in choirs her whole life. . . .

So has Callista.

In debates and stump speeches, Gingrich’s religious conversion is the centerpiece of his maturation as both man and politician. Callista’s participation in this choir is a large part of that narrative. After their marriage in 2000, he accompanied her to Mass regularly, first to watch her sing, and then, later, for reasons of his own.

“I’m genuinely surprised by what a comfort the church has been,” he said. “It’s comforted me in ways I would have never expected 25 years ago.”

Throughout their ups and downs in the public eye, Callista’s devotion to this choir hasn’t wavered. She still arrives on time to Thursday rehearsals, overdressed in stately suits. She still sings at noon Mass, even when she has to walk the Kennedy Center’s red carpet hours later. But to this close-knit group of singers, the candidate and his wife are just their friends “Callista and Newt,” a couple juggling responsibilities like everyone else. Even the newest young members of the choir look upon Callista as a talented musician, whose husband just happens to be running for president.

“I do worry if he wins . . . would she still be able to sing here?” said Crossley Hawn, 23, a soprano who speaks about Callista as though she were a favorite aunt.

“My grandmother keeps asking me, ‘If he wins, you think you’d have your Christmas party at the White House?’ ” laughed Matthew Mueller, 28, a tenor and graduate student at Catholic University. “But really, this is where she fits into the crowd. We all have families and jobs, and we talk about them with each other. We’ll ask, ‘How was school? How was your day at work? And Callista, how was your evening at that televised debate last night?’ ”

A musician, first

Like her husband, Callista Gingrich greets strangers with a stiff, outstretched hand. She’s guarded in introductions, controlled in the way a political spouse must be, particularly when the public still associates this one with a marriage that began as an affair. For more than a decade, she has maintained a visible yet silent presence beside her husband.

But in this imposing church, empty at 10 p.m. save for a few fellow singers, the artifice of campaigning slides off. She’s relaxed, approaching comfortable — and happy to explain why she joined this choir over a decade ago.

“They needed altos,” she says candidly. The lifelong Catholic offers no rehearsed sound bite on the strength of the liturgy or diversity of the congregation. This choir simply needed her range, so a friend persuaded her to audition. “I was already singing at the Capitol Hill Chorale, and I was very happy there, but I auditioned anyway.”

Callista is a musician, first. She doesn’t say it in those words exactly, and might even argue with that description, but her carriage changes when she’s talking about the piano, an instrument she started playing in the third grade. She now plays French horn in the City of Fairfax Band, which, unlike the choir, is an all-volunteer band, partially funded by the Gingrich Foundation.

“She’s a fine musician,” said Peter Latona, 43, who has served as the choir’s conductor and the shrine’s music director since 2001. “As you can probably tell from her appearance, she’s very particular about details.”

“Callista, for as put-together as she is all the time, she’s very down-to-earth,” Hawn said. “She remembers what you tell her. And that’s what I’ve noticed most. She’s always paying attention.”

Born and raised in Whitehall, Wis., she attended Luther College in Decorah, Iowa, on a music scholarship. The school counts Steven Hendrickson, principal trumpet of the National Symphony Orchestra, and Marty Haugen, a composer of liturgical music, as alumni of their music program.

“I was their diversity statistic,” Callista laughs, a joke she has probably cracked for decades, since the Catholic population of her alma mater hovers around 15 percent.

Callista’s training pinpoints exactly what makes the choir at the shrine so distinct from other choirs at Catholic churches.

It is unabashedly good, routinely cited as one of the best Catholic choirs in the nation.

Catholic choirs don’t always receive such acclaim.

Poor musical quality is a relatively new development in Catholicism, a religion that patronized the likes of Bach, Haydn and Scarlatti. Some blame modernization. When the Mass changed in the early 1960s, the music changed, too.

Others blame funding cuts. In recent decades, sacred music, not required at Catholic Mass, has become less traditional, less serious, easily produced by guitars, bongo drums and eager volunteers who try really, really hard.

“Music is a priority here,” said Mon­signor Walter R. Rossi, rector of the shrine, who arrived the same year as Latona, in 1997. “This is a pilgrim church. A tourist church. And everyone who comes here wants to come here because they find the worship fulfilling.”

Latona’s choir embraces more traditional sacred music. There are no hymnals in the basilica’s pews. Latona prefers to curate the musical selection every week, selecting pieces that span styles and centuries. Palestrina. William Byrd. Thomas Tallis. Arvo Part. Even preferred composers must pass his strict litmus test for sacred music.

An organist and composer, Latona selects music with academic and formulaic precision. Even renowned composers, such as Mozart, often fail to meet Latona’s standards. “Mozart tends to bring you out of church,” he says reluctantly. “It reminds me of a classical music station too much. A piece has to have intrinsic beauty, but there are other factors. Is it the right text? The right key? How will it sound in this space?”

The shrine has the only all-paid professional choir in the Catholic Archdiocese of Washington. All members are paid the same amount, $80 for each Mass and rehearsal, and must re-audition every year. Some members sing in multiple local choirs, and although most members are some denomination of Christian, they are not required to be Catholic.

In 2005, Latona led the choir to Rome to record an album in honor of Pope John Paul II. In 2008, it performed there again at the International Festival of Sacred Music and Art. The Gingriches attended both events.

“We treat these trips as a pilgrimage,” Latona said. “We sang Masses every day, and just to be in these historical basilicas that evoke the whole tradition, coupled with this beautiful music . . .” he trails off. “The whole thing comes together. But, of course, the Roman way is to have extended dinners and lunches. [Newt] could relax. He wasn’t Mr. Speaker there. He was just ‘Callista’s husband,’ and a good friend of the choir.”

Conversion of a candidate

There’s an elephant in the church, a question that those who know the Gingriches are reluctant to ask. Spouses sometimes lead their spouses to conversion. But can music?

In popular culture, images of choirs belting out Handel’s “Hallelujah Chorus” are sometimes associated with good fortune and epiphany. But is there a link between conversion and sacred music?

That question makes some Catholics nervous. It oversimplifies everything. Choirs don’t convert people or presidential candidates.

“Music can help with conversion,” said Rossi, who served as Gingrich’s sponsor, alongside Callista, in 2009. “I’m not sure it’s the entry point or cause of. Conversion is a lifelong process. It’s rare that people have experiences like Saint Paul, who got knocked off his horse on his way to Damascus.”

“Did [Newt] hear the choir sing a piece of music and have a ‘Road to Emmaus’ moment? No. Obviously, lots of thought and life experience goes into that decision,” Latona said. “However, had he followed Callista to a Catholic church where the liturgy was poorly done and the music was abysmal, would he have converted? I don’t know. The chances of that happening are less.”

Still, by Gingrich’s own account, the choir and Callista played significant roles in his spiritual life, along with Pope Benedict XVI’s visit to Washington and various books by religious scholars. But this convert candidate did say the music “brought me here.” That must be a point of pride for Latona.

“I haven’t really thought about it. I suppose if I did, it would make me feel really good” said Latona, pausing briefly to smile. “But he is just one person. I’d like to reach many, many more.”

WHUT will broadcast the choir performances Dec. 24 at 11 p.m. and Dec. 25 at 9 a.m.