Many U.S. congregations have grown so large that the term "megachurch" no longer seems adequate. So some observers have created a new category: the gigachurch.

Where megachurch refers to congregations with an average of 2,000 or more worshipers every weekend, gigachurch refers to those with 10,000 or more, said Texas-based church consultant Bill Easum, adding that the rising number of large congregations reflects a major shift in worship patterns.

"Today, fully 3 million church attendees go to a megachurch vs. 897,000 only 10 years ago," Easum writes in the current issue of Outreach, an evangelical magazine published in Vista, Calif. Thirty-five of the congregations on the list of megachurches did not even exist a decade ago. "The landscape of the Christian church is changing faster than at any other point in American history."

The flagship church of this change, in terms of size and speed of growth, is Lakewood Church in Houston, said John N. Vaughn, a leading analyst of the megachurch phenomenon. Lakewood posts an average attendance of 25,060 per weekend -- nearly twice its attendance five years ago and 8,000 more than Willow Creek Community Church near Chicago, which two decades ago set the standard for megachurch development.

With its move next spring to a 16,000-seat sanctuary, the $73 million remodeled Compaq Center -- former home to the Houston Rockets -- Lakewood is on track to become the first U.S. church to surpass 30,000 in attendance, Vaughn said.

Since the mid-1990s, the number of reported megachurches has nearly tripled, from 300 to 840, according to figures compiled by Vaughn and presented in Outreach's May/June issue. Reasons include the surge in evangelical Christianity; the trend toward high-energy and high-tech worship; national seminars for church leaders on how to improve programming; and the range of small-group opportunities for Bible study, emotional support and other purposes that a large congregation can provide.

Thirty-one Protestant and nondenominational churches have reached the 10,000 attendance mark, and one Washington area church, the 10,000-seat Jericho City of Praise in Landover, is among them. Jericho's pastor, the Rev. Betty Peebles, is the only woman to head one of the country's largest 100 churches.

McLean Bible Church, which will move into a 2,400-seat sanctuary as early as next month, is close behind, with 8,389 worshipers a weekend. Ebenezer AME Church in Fort Washington and From the Heart Church Ministries in Suitland are the area's next-largest congregations, each with about 7,000 worshipers.

Regional churches on the list include Jerry Falwell's Thomas Road Baptist Church in Lynchburg, with 7,500 attendees, and New Psalmist Baptist Church in Baltimore, with 7,000.

Those numbers -- most compiled as recently as mid-April -- already could be low, said Vaughn, an independent researcher and founder of Church Growth Today, a consulting firm in Bolivar, Mo. Some of the country's fastest-growing congregations are adding worshipers at a rate of dozens or hundreds per week, he said in a telephone interview.

Weekend figures represent non-duplicated attendance at Sunday and Saturday (or Friday) services, including overflow rooms and off-site locations with video hookups, and children and youth programs. The self-reported numbers are provided by denominational offices or individual churches, said Vaughn, who began compiling such information in 1980 and has thousands of churches in his database.

Vaughn measures size and vibrancy by attendance -- he refers to John Wesley's axiom that if you're not active, you're not part of the group.

The Nashville-based Glenmary Research Center, which every 10 years publishes the widely respected "Religious Congregations and Membership," lists membership figures along with numbers of "adherents," which refers to people who attend a church regularly but have not joined.

But a growing number of researchers find membership figures unreliable. Churches of all denominations are notorious for not updating membership rolls, whether by neglect or design -- deliberate falsification to boost membership figures, said Dean Hoge, director of the Life Cycle Institute at Catholic University and author of numerous studies on Catholic and Protestant practices.

"Attendance is a better way of doing it," the sociologist said. "It doesn't depend on the definition [of what a member is]. If you're there, you get counted."

Richard Houseal, researcher with the Church of the Nazarene and president of the Association of Statisticians of American Religious Bodies, said that although attendance provides a more accurate accounting of activity, using that yardstick has its downsides. Attendance varies widely by season, especially at Christmas and Easter, and deemphasizing membership could be changing the expectation that a person make regular contributions, he said.

Vaughn said that large size does not mean better quality. About 80 percent of an estimated 400,000 U.S. churches have weekend attendance of fewer than 200, he said, and most of those congregations serve their communities well. About 50,000 small churches emerged in the 1990s.

At the same time, more Protestant churches than Catholic churches -- whose membership and attendance are largely determined by geography -- have experienced exponential growth. Catholics typically belong to the parish church nearest their residence.

For that reason, the 66 million-member Roman Catholic Church in the United States, the largest denomination in the country, for generations has had thousands of parishes that meet the definition of megachurch, or attendance of 2,000 or more on weekends, he said. But Catholic parishes are typically subdivided when they reach a certain level, so very few have attendance of 10,000 or more, he said.

Vaughn offers a cautionary note for American Protestants who are puffing their chests with pride. Attendance at Lakewood, the country's largest and fastest-growing church, pales in comparison with that of the world's largest church, the 800,000-member Yoido Full Gospel Church in Seoul. Vaughn, author of "The World's 20 Largest Churches," estimates Yoido's weekend attendance at more than 100,000 in three large facilities.

At least nine other non-Catholic churches in Korea report more than 20,000 in attendance, as do several churches each in Chile, Argentina, Nigeria, El Salvador, Indonesia and the United States, he said. A total of 25 churches in those countries, Egypt and the Philippines report weekend attendance of 10,000 to 20,000, he said.

Lakewood Church in Houston has a weekend attendance of more than 25,000, making it the largest U.S. church. Worshipers meet in the old Compaq Center, soon to be their new home. Pastor Joel Osteen, 41, assumed leadership of Lakewood Church in 1999 after the death of his father, church founder John Osteen. In the five years since Joel Osteen took over, the church has nearly doubled its weekend attendance. Attendees at Jericho City of Praise Church in Landover, which draws 10,000 worshipers each weekend, gather for a gospel concert.The Rev. Betty Peebles of Jericho City of Praise.