(FORTUNE Magazine) – ''For big churches, the traditional denominations have outlived their usefulness. They're like labor unions.'' So says Fred Smith of the Leadership Network, a resource group for large churches founded in 1984 by Texas businessman Robert Buford ''to give something back to the Lord.'' Large interdenominational churches are the fastest-growing type in the U.S. In 1984 only 100 American churches averaged more than 2,000 worshipers on Sunday; that number has doubled, and some 10,000 churches now have an average attendance of 1,000 or more. Yet, says Smith, ''they're always surprised when they discover each other.'' Buford is CEO of Buford Television, which owns WMBB-TV in Florida and is involved in 120 cable franchises; Smith, a divinity graduate of Harvard, once taught school. They put on two dozen seminars each year. Peter Drucker and Lyle Schaller have been among the experts who participate. Next year: pollster George Gallup. In Buford's view, denominations and seminaries support an obsolete 19th- century model of church organization. That church, he says, was ''like a corner grocery store.'' It served a blue-collar or agricultural constituency that had little free time, and it had one pastor for 200 or fewer people ''because that was as many as the pastor could keep up with.'' As the country changed, the neighborhood church had to make way for what he calls parachurch organizations. Buford compares them to national chain stores, specializing in one part of church work: the Billy Graham Crusade, focusing on evangelism; Alcoholics Anonymous; youth groups like the InterVarsity Christian Fellowship. ''The successor to both,'' Buford claims, ''is the large church. It's like a shopping mall. It contains all the specialized ministries of parachurch groups under one roof.'' It is often suburban, and its members are looking for a sense of community in a place that is often far from where they grew up. Churches of this sort tend to be conservative theologically, but Buford, an Episcopalian, and Smith, a Southern Baptist, don't see theology or doctrine as the primary forces behind their growth. According to Smith, ''These churches grow because they have identified their business differently. They see themselves as delivery systems rather than as accumulators of human capital.'' The aim is more to push ministry out into the community than merely to get people to come to church. One thing they deliver better than small churches, paradoxically, is intimacy. Says Smith: ''Large churches are honeycombed with small groups -- cells, sharing groups, discipleship groups -- organized around a subject like caring for small children or growing older.'' Buford and Smith find that the leaders of such churches need help most in three areas: forming a vision for the organization, handling staff, and maintaining spiritual vitality in the face of administrative demands or, conversely, the temptations of stardom. Like entrepreneurs everywhere, they worry about succession, a problem that will grow in the next few years. One problem the free-standing churches don't have: the cost of supporting the regional and U.S. headquarters of a big denomination. Next year one large Episcopal church in Manhattan could be stuck with an assessment of more than $400,000 -- nearly 20% of its 1989 income -- for the diocese and the national church.