It is a debate that could change the Presbyterian Church (U.S.A.) forever: whether to allow leeway on the ordination of gay clergy and lay elders and deacons.

A national assembly was poised to decide Tuesday on a complex proposal giving flexibility in deciding fitness for office to local congregations — which choose lay officers — and regional presbyteries, which ordain and approve pastors.

In a plan devised by a special task force, Presbyterians would keep on the books a church law that says all office-holders must observe either fidelity in heterosexual marriage or else chastity in singleness.

The panel spent years considering the issue before introducing the proposal, which is designed to hold together Presbyterians who support full equality for homosexuals and those who believe change would violate biblical teaching.

U.S. Presbyterians have been publicly divided on sexual morality since a 1970 assembly. Some observers think the wrangling has been one factor in the denomination's disastrous decline in membership.

Conservatives see dire results for the denomination of 2.3 million and 11,000 congregations if the plan is approved.

"It will not be business as usual. It cannot be. Consternation will be just too high," said the Rev. Jim Berkley, Presbyterian specialist with the Institute on Religion and Democracy. "We will cease to be the Presbyterian Church most of us knew."

The Rev. Michael Walker, executive director of Presbyterians for Renewal, said "the unity of the church is at stake. This may be a vote to keep the church together or to vote for division."

But the Rev. Jack Rogers, a theologian and former titular head of the denomination who favors gay ordinations, said such concerns are overblown.

"There will be no mass exodus. We've heard all these threats before. ... This is not an issue to divide a denomination over. It doesn't touch the core of the faith."

Rogers said if the flexibility plan is approved, "a few" gays who live with partners will be ordained, "but it isn't going to be any mass thing."