In fast-developing Chester County, there is a growing Catholic presence that is plain to see, and another that is not.

One is manifest in the 30 parish churches and 14 parochial schools set among sprawling fields of subdivision homes. They brim with 153,000 suburban church members, a 60 percent increase since 1990.

The beating heart of the other is tucked into an Avondale strip mall, in basement rooms lush with polychrome crucifixes and images of the Virgin Mary. Behind a travel agency and a tanning salon, it is nearly invisible from Route 41. But if you are a Latino immigrant in need of food, clothing and shelter, you soon find your way to La Misión Santa María, Madre de Dios - and into the gravity field of the American Catholic Church.

The Philadelphia Archdiocese opened this social-services outpost in 1992, when it counted 2,000 Hispanic Catholics in the county's south end, the mushroom capital of the world. Most were Puerto Rican men who labored in the dank sheds while their families waited 1,200 miles away.

By 2004, the number had more than quadrupled to 9,500. Nearly all were Mexican and Mexican American, with many young couples, and many babies. "We must be well past 10,000 by now," said Msgr. Francis Depman, the director. "Last year, we had 348 baptisms."

Those drawn to the mission are a small portion of the five-county archdiocese's Hispanic Catholic population, estimated at 150,000 but possibly as large as 190,000.

They are an even tinier fraction of the 30 million buoying the rolls of the U.S. church.

Since 1970, Latinos have accounted for a remarkable 90 percent of the church's growth nationwide. They already make up 42 percent of the Catholic population in this country, and if their immigration and birthrates stay at current levels, they will be the majority by midcentury.

The nation's bishops are protesting congressional efforts to turn the immigrant tide. But at the same time, they acknowledge that their church is generally ill prepared to meet its full force.

Often poor, conversant only in Spanish, and - in the case of as many as nine million - undocumented, Latino Catholics can be hard to reach, and harder still to hold.

Rare is a place as resourceful as La Misión Santa María, one of a kind in the archdiocese.

Every day, between 50 and 100 people come to it for the basics of survival, as well as legal and medical assistance and translation services.

On a spring weekday, a muscled young Mexican stood nervously with his wife and toddler son at the desk of Janette Gaytan, the social services director.

"Sólo su nombre está bien," she assured them. "Just your first name is OK."

Reluctantly he answered, "Roberto." His wife was Soledad, their 3-year-old child Domingo.

"Estamos buscando un lugar para vivir," he said. "We are looking for a place to live."

"Drive around and look for 'for rent' signs," Gaytan told them in Spanish, "and write down the phone numbers. Then come back and I will make the calls for you."

They disappeared through the glass doors, with no mention having been made of religion, no pressure applied to sign up.

"We don't want them to think they have to go to church for us to help them," Gaytan said. "But they will be back."

A wave of change

Roberto and Soledad have far more influence than they might imagine.

While nearly half of Latinos in the United States are not fluent enough to follow an English-language Mass, they are more likely to shape the future of the American Catholic Church than all its other ethnic groups - including those that have led it during the last 200 years.

This epic shift is grist for scholars' speculation. There are those who foresee Latin religious expression eventually defining the U.S. church, and those who predict that generations of immigrant offspring will be homogenized, as the Irish, Poles and Italians were a century ago. Others envision the evolution of two separate, culturally distinct churches.

R. Stephen Warner, an authority on religious communities and immigration, sees them slowly meeting partway.

Latinos are "Americanizing, and at the same time, I think, the church is moving toward them," said Warner, a sociology professor at the University of Illinois at Chicago. The result will be "a little less puritanism, a little more Pentecostalism, and a lot more exuberance."