Are the mainline Protestant splinter churches a new Reformation or old news?

There’s a popular saying in church-planting circles: It’s easier to make babies than to raise the dead.

That principle applies to denominations as well, said the Rev. Paul Detterman, who helped found the Evangelical Covenant Order of Presbyterians in January.

“We thought it was easier in the long run to create something new rather than to keep on trying to modify existing forms,” he said.

The “existing form,” in Detterman’s case, was the Presbyterian Church (USA), which remains the nation’s largest Presbyterian denomination despite a decades-long plunge in membership.

The ECO may steepen that decline. Thousands of conservative Presbyterians, upset over the PC(USA)’s vote to lift its ban on partnered gay and lesbian clergy last year, are eyeing the new group. Planning for the ECO, which will not ordain sexually active gays and lesbians, preceded the gay clergy vote, Detterman said.

Nonetheless, the ECO represents the third new mainline Protestant denomination since 2008 to split from a national church following votes to permit partnered gay clergy.

The Anglican Church in North America formed in late 2008, five years after the Episcopal Church consecrated an openly gay bishop in New Hampshire. In 2010, a year after the Evangelical Lutheran Church in America voted to allow partnered gay and lesbian clergy, conservatives formed the North American Lutheran Church.

The question now is whether these breakaway groups signal a seismic shift in American Protestantism, or just a few fissures in the theological terrain.

Leaders of all three new denominations say the gay clergy issue was only the breaking point for conservatives, after years of dissatisfaction with overbearing bureaucracies, membership losses and liberal theology. Pessimistic about changing that course from within, some conservatives jumped ship instead.

“When orthodox and conservative Christians made homosexuality their flash-point issue, and they lost those struggles, in many ways they had no choice but to create these new structures,” said Mark Tooley, president of the Institute for Religion & Democracy, a conservative Washington-based advocacy group.

In some ways, the rifts are nothing new. American Protestants have been splintering since Roger Williams left Plymouth Colony in the 1630s, said Nancy Ammerman, a sociologist of religion at Boston University.

Yet the schisms counter a 20th-century trend in which ethnic and regional Protestant groups merged to form big-tent denominations such as the ELCA and PC(USA).

“What we may be experiencing at this point is the limit of that movement to draw a lot of diversity under one umbrella,” said Ammerman, author of “Pillars of Faith: American Congregations and Their Partners.”

Archbishop Robert Duncan, ACNA’s leader, said the new denominations herald a burgeoning movement.

“There is a Reformation going on in the Christian church, particularly in the West, and particularly in the mainline Protestant denominations,” he said. Duncan’s ACNA seeks to supplant the Episcopal Church as the U.S. branch of the worldwide Anglican Communion.