LOUISVILLE -- America's mainline Protestant churches should not blame their staggering membership decline on anyone but themselves, suggested church leaders and theologians who gathered here for a three-day conference on the future of the mainline bodies.

Neither the growing fundamentalist churches with their appeal to religious and moral certitude nor the secularizing impact of the wider culture are the villains responsible for the losses afflicting the more liberal Protestant denominations, according to the latest research of scholars who have studied the 30-year decline.

Mainline worshipers "don't storm out of their fellowships in righteous anger and into the waiting pews of the independent conservative Christian congregation across the street," said the Rev. Elizabeth Nordbeck, a United Church of Christ clergywoman and dean of Andover-Newton Theological Seminary near Boston. "Instead, they simply drift away in apathy."

"It appears that the fundamentalists . . . aren't really our enemy," she said. "The enemy is us."

One of the most comprehensive studies of the diminished mainline populations was based at Louisville Presbyterian Seminary, where the conference was held. In a three-year effort, 60 researchers involved in more than 50 projects conducted an analysis of the Presbyterian Church (U.S.A.).

New research shows that "the church is not simply a victim" of sociological trends and shifting demographics, the Rev. Dorothy Bass, the keynote speaker, said in an interview last week.

Results of some of the Presbyterian studies offered no "quick fixes" for the mainline dilemma, said Bass, a United Church of Christ clergywoman and visiting theologian at Valparaiso University in Indiana.

The seminary research focused on the Presbyterian Church, which has experienced a drop in membership from 4.25 million to fewer than 3 million members since 1965. But the Presbyterian experience is typical of other mainline denominations that historically carried a lot of clout, such as the Episcopal Church, the United Methodist Church, the Evangelical Lutheran Church in America and the United Church of Christ -- all of which have lost significant numbers of members.

A lower birth rate and the failure of denominations to hold onto the distinctive identities that encourage traditional membership loyalty are among other reasons suggested for the loss of membership which, Nordbeck said, highlights the "irony" of the mainline churches becoming a sideline religious phenomenon.

The Rev. Craig Dykstra, vice president for religion at the Lilly Endowment in Indianapolis, which funded the studies, said the structure of U.S. mainline churches has mirrored society and evolved in much the same way the country has.

Leaving their roots in Europe, where the churches often were state-sponsored, the denominations in the United States were loose-knit structures that lacked a central staff and national focus. The need to adapt to better meet people's needs and national goals increasingly changed the churches into corporate-styled "religious conglomerates," the Lilly official said. But that successful corporate model broke down in the 1960s, partially as a result of the membership loss, and the mainline churches began to "look less like a corporation and more like a regulatory agency" issuing decrees and regulations.

Instead of looking for imaginative means to educate and encourage moral behavior in their people, these denominations issued statements demanding such behavior, Dykstra said.

The health of a denomination is not solely a function of its numbers, said Nordbeck. She said Presbyterians are giving more money per person to their church than before. Nevertheless, she said membership losses "cannot and hopefully will not be ignored simply because we have found a new way to make uneasy peace with our shrinkage. Realizing that we're in a state of crisis may lead to some renewal," she said.