Those on both sides expect the Episcopal Diocese to vote today to secede from the U.S. denomination and join an Anglican province in South America -- but with at least 17 of approximately 73 parishes choosing to remain in the Episcopal Church.

In the first of two required votes, last year the laity voted 118-58 and clergy voted 109-24 to secede. While some think a reversal is possible, no one is predicting it.

Opponents were more optimistic earlier, when some church leaders who admired Pittsburgh's then-Bishop Robert Duncan were nevertheless wary of secession, said Rich Creehan, spokesman for Across the Aisle, a group for those who intend to remain Episcopal. But the Sept. 18 vote of the Episcopal House of Bishops to remove Bishop Duncan changed that.

"They saw that action by the House of Bishops as an insult and said they didn't want to be part of people who acted like that," Mr. Creehan said.

The plan to join the Anglican Province of the Southern Cone, which covers six nations in South America, reflects differences over theology, biblical authority and sexual ethics between the conservative diocese and the national church. The 2.3 million-member Episcopal Church is the U.S. branch of the 77 million-member Anglican Communion. Most Anglicans live in the global south and many of their leaders are theological conservatives who have invited conservative Episcopalians to realign with them. The Episcopal Church calls that a violation of church law, and says it owns all the property.

The vote, to be conducted at St. Martin's Episcopal Church, Monroeville, requires a simple majority.

Bishop Duncan, now a bishop-at-large of the Southern Cone, is a diocesan consultant. He will sit with other staff but will not lead worship or the business meeting, said Deacon Peter Frank, spokesman for the diocese. If the majority secede, they will give 30 days notice for another convention at which they are expected to re-elect Bishop Duncan, he said.

Meanwhile, the sole person on the eight-member Standing Committee known to oppose secession will become the default authority of a continuing Episcopal diocese. The Rev. James Simons, rector of St. Michael of the Valley in Ligonier, said he will immediately appoint at least two others to join him on the continuing Standing Committee and give 30 days notice for a diocesan convention to elect new leadership. But he believes the vote to secede could fail.

"I've talked to deputies [to the convention] who haven't wanted to be disrespectful to Bishop Duncan and have never said anything publicly. But they've confided to me that they can't vote for it a second time around," the Rev. Simons said.

If the vote fails, he said, the diocese must elect a new bishop and work hard to heal wounds. But it would be "a whole lot easier administratively" than the confusion and lawsuits that seem likely if the vote is for secession, he said.

Deacon Frank vehemently disagreed, saying parishes would leave separately for a half-dozen Anglican provinces.

"The vote not passing is a very scary proposition. Instead of having two Anglican groups in Pittsburgh, it would be very easy to see having three or four," Deacon Frank said.

At the convention, opponents of secession plan to argue that the vote violates church law. The Rev. Simons said one group plans to challenge the validity of one of four mission churches slated to be voted on for parish status prior to the secession vote. Parishes have a vote, missions do not.

Across the Aisle says it has received official notice from 17 parishes that intend to remain Episcopal. Deacon Frank said the diocese is aware of 16.

"We expect that there will be more," Deacon Frank said. "It looks like somewhere around two-thirds one way and one-third the other."

At least 10 parishes are believed to be deeply divided, with clergy, groups of laity and the voting deputies having different loyalties.

"If they decide they are in the realignment camp now, and later change their mind, that's no problem for us," the Rev. Simons said. "We'll welcome anybody back at any time."

If realignment passes, parishes will have two years to decide which diocese to align with, Deacon Frank said. The two-year window is probably unworkable, the Rev. Simons said.

"Practical decisions have to be made much sooner. When they pay next month's assessment, who are they going to make the check out to?"

The Rev. Simons said that someone who is already a bishop will likely serve as an interim while the continuing diocese searches for a new bishop. Although he expects to ask national church leaders which retired bishops are available, the interim bishop will be chosen by local people, he said.

Some local opponents of secession have already filed a lawsuit over property, and the national church has also threatened to sue some realigned parishes. But litigation isn't the only reason that a Southern Cone diocese will keep the name "Episcopal Diocese of Pittsburgh," Deacon Frank said.

"We really do see ourselves as the Episcopal Diocese of Pittsburgh making a decision under our own rules. We are not leaving. There are many people from our perspective that believe this is a step to maintain our heritage, not abandon it," he said.