The St. John Paul II Pastoral Center, a Roman Catholic mission, sits at the rough end of a former strip mall in the shadow of an Arby's. The space, church leaders say, was once used as a nightclub and movie theater, a history now hidden by multiple coats of paint, pews brought in from other congregations, and a stone-and-wood shrine to Our Lady of Guadalupe, the patroness of the Americas especially revered by Mexicans.

This mission, in the Archdiocese of Atlanta, was built in a hurry, to serve the many Latinos who labor at the poultry processing plants that form the economic backbone of Gainesville. On a recent Sunday, worshippers spilled onto the sidewalk in rows two and three deep, and by the end of the weekend, 5,000 people had attended Mass here.

Evangelicals have set up shop here, too. Georgia is Baptist country and a Bible Belt stronghold where Catholics had a small footprint until the latest immigration boom. The Rev. William Canales, the cherubic, Nicaraguan pastor of the mission, noted with a twinkle in his eye that a Protestant preacher in the same mall had recently moved on.

"The Catholic Church in Gainesville — we are waking up now," Canales said, on the eve of the first visit to the United States by Pope Francis, the first Latin American pontiff.

Francis will arrive in the U.S. on Sept. 22, carrying the hopes of many for what he might do for American Catholicism. But few of these goals have as much urgency for church leaders as affirming the place of Latinos in the church and inspiring them to stay in the fold.

About 38 percent of adult Catholics in the U.S. are Latino, according to the CARA research center at Georgetown University, and they are already the majority in several dioceses.

Their numbers are increasing at the same time a steady stream of American Catholics overall are leaving the faith. Immigration and the high birth-rate for Latino Catholics have more than made up for the losses, helping the 68-million-member denomination continue to grow.

Yet, Latinos aren't sticking with the church the way they once did. In 2006, about eight in 10 Latinos who were raised Catholic stayed in the tradition as adults. That figure dropped to seven in 10 last year, according to CARA. Like many Latin Americans back home, U.S. Latinos are joining Pentecostal movements, or abandoning organized religion entirely, in numbers significant enough to raise alarm among U.S. bishops.

"One of the challenges for Latino immigrants is they continue to show up in places where there's not a Catholic Church nearby," said Mark Gray, the Georgetown center's polling director. "Sometimes, they end up in an evangelical church."

Georgia is one of the more dramatic examples. The Catholic population here had been so small historically that the state didn't have a diocese until 1936 in Savannah, nearly 150 years after the first U.S. diocese was established in Baltimore. The Atlanta diocese is even newer, created in 1956 with just 24,000 parishioners.

Now, Peter Faletti, Atlanta archdiocese director of research and planning, is scrambling for space. He has been renting schools, former movie theaters and defunct car dealerships so he can turn them into worship sites. Even so, he says services fill to capacity within weeks. In Lilburn, an Atlanta suburb, Our Lady of the Americas draws 10,000 mostly Latino Mass-goers each weekend and is still growing.

"We have Hispanic Catholics who aren't being served because they can't get in the door," Faletti said.

Non-Hispanic professionals relocating to the Atlanta area from the North and Midwest have helped increase Catholic numbers in recent years, but Latinos are the main drivers of the boom. From 2000 to 2011, the Latino population doubled in Georgia, putting the state in the Top 10 for Latino growth in that period, according to Pew.

Latinos and whites each make up about 44 percent of the 1 million members of the Atlanta archdiocese, and Latinos are on track to eventually become the majority.

"People are excited about the growth. They recall the days when they were such a minority presence that they were all but unnoticed," said Archbishop Wilton Gregory. "The challenge is that we not only have to provide physical space for the communities who are expanding, but we also need to develop a spirit of inclusion."

This is an area where the pope, an Argentine native, will help, church leaders say.

Los Angeles Archbishop Jose Gomez, the highest-ranking Latino in the U.S. church, whose archdiocese, 70 percent Latino, has been at the forefront of advocating for immigrants, said the role of Latinos "is a big part of the story of the pope's visit." In Washington, the pope will canonize 18th-century Spaniard and Franciscan missionary Junipero Serra, who evangelized the territory that would become California. Gomez called the canonization a "historic moment in the life of the Hispanic people" in which the pope is calling on Americans to reflect on "our legacy as immigrants."

"He knows the face of the church is changing. He knows the country's Hispanic Catholic heritage. He knows how important Hispanics are for the future of the church," Gomez said.

Atlanta Catholic leaders say no one in the church anticipated how many immigrants would make Georgia their home. Jairo Martinez, a Colombian who leads Hispanic ministry for the archdiocese, said he was stunned they were choosing the state over Florida or California.

"Georgia was not a place for people to come. It was, for us, a little of a no-man's land," said Martinez, who originally came to Atlanta with Coca-Cola, where he was an executive. "The archdiocese was not prepared. There weren't Masses, services or priests who spoke the language."

The surge in construction jobs ahead of the 1996 Summer Olympics in Atlanta brought a wave of mostly Mexican immigrants. More came to work in the carpet-making industry in Dalton, near the Tennessee line, and in the poultry plants in Gainesville, northeast of Atlanta.

Canales noted the pope's exhortation for priests to be close to the marginalized and be "shepherds living with the smell of the sheep." Canales joked, "I smell like the chicken here."

Monica Oppermann, who works in the archdiocese office for teaching and evangelizing, said she watched as an apartment complex near her parish began to fill with Latino families. A priest enlisted a Spanish-speaking nun, along with Oppermann, who is from Mexico to help the newcomers.

Martinez said Latinos would call his office saying they'd been praying the rosary with other families in someone's house because they couldn't find a Mass. The archdiocese started a Spanish-language radio broadcast, now called Nuestra Fe, or Our Faith, to try to fill the void, and sent representatives abroad to find Spanish-speaking clergy willing to relocate.

The archdiocese, like dioceses across the U.S., is still badly in need of Spanish-speaking and bilingual priests. But one out of every three or four Masses in the archdiocese are now in Spanish, Faletti said.

Amid all the changes, Gregory acknowledges some friction over the archdiocese's new diversity.

Church leaders are trying to bridge the cultural divides, but just like the situation for previous generations of Catholic immigrants arrived in America from Italy, Ireland and elsewhere, relationships between different ethnic groups — within and outside the church — aren't easily built.

Atlanta's white Catholics are wealthier and better educated, including about Catholicism. Some of the Latinos hadn't studied beyond elementary school before they came to Georgia, and even though they participated in festivals and services at their churches back home, weren't thoroughly taught about the religion.

"In my homilies, I try to do catechesis — biblical explanations — so people understand what's going on," said the Rev. Mark Starr of St. Clare of Assisi Mission in suburban Acworth, who learned Spanish on an eight-week immersion course in Mexico but says he's not always confident with the language. "I'll explain where these Mass parts come from scripturally, or explain the prayers that the priest prays in silence. I've had people come up and say, 'I never knew that.'"

For Mexicans especially, being part of the church means participating in festivals, such as the annual feast of Our Lady of Guadalupe, or being part of religious movements, including the spirit-filled Catholic Charismatic Renewal, that aren't necessarily rooted in a parish, where they could connect with people from other backgrounds.

And many of the Latinos in the archdiocese are in the country illegally, bringing the polarizing debate over immigration policy into parish life in an immediate way. This past summer, a pregnant woman from El Salvador who is in the country illegally sought sanctuary in the Lilburn church from federal immigration authorities. Atlanta church officials believe it was the first time anyone had sought sanctuary over immigration status in their archdiocese. She left the church soon after and is receiving help from a lawyer, the archdiocese said.

"These people who are here and may be undocumented are loving Catholic people and we have to welcome them and make sure people understand the Gospel — and that the church has always stood with people who are new arrivals," Gregory said.

Guzman Carriquiry, vice president of the Pontifical Commission for Latin America and a friend of the pope's, said Francis on the U.S. trip will uphold Latinos not as an "add on" to church life, but at the heart of American Catholicism, in a message meant to carry throughout the country and beyond.

The plight of immigrants, and the need for wealthy nations to be generous and welcoming to newcomers, will be a constant theme throughout Francis' visit. He is expected to discuss immigration in his Sept. 24 remarks to a joint meeting of Congress. Francis will give several talks in Spanish and is scheduled to meet immigrants in Washington and at an East Harlem Catholic parish in New York, before heading to Philadelphia.

At the St. John Paul II Pastoral Center in Gainesville, mission members are hoping for some local inspiration from the papal visit. They have taken up an activity more often associated in the U.S. with evangelicals: going house by house through the city inviting Latinos and others to Mass. Canales said one woman was so stunned to see Catholic evangelizers on her doorstep, she asked several times whether they weren't, in fact, Protestant.

Parishioner Jose Vera, who has worked in local poultry plants for about 20 years, said he especially appreciates Francis' emphasis on warmth and compassion as a way to bring fallen away Catholics back to the church.

"We don't have to be an expert to talk about God. We just go there and give the biggest smile to the person," Vera said after mid-morning Mass. "We don't need a big school. We don't need to learn the whole Bible. You just have to hear what they have to say."