The other two homosexual candidates are the Rev. Michael Barlowe, the California Diocese's development officer, and the Rev. Bonnie Perry, rector of All Saints Episcopal Church in Chicago.

The vote among laity and clergy from 86 Episcopal churches representing 27,000 parishioners in the Bay area starts just before 9 a.m. at Grace Cathedral. The diocese will post vote totals on its new Web site, Episcopalbayarea.org, which was set up just in time to handle an expected deluge of visitors from around the world.

The nominee who is elected must be ratified by the Episcopal General Convention, which meets in June in Columbus, Ohio.

The Rev. Paul Zahl, dean of the conservative Trinity Episcopal School for Ministry in Ambridge, Pa., likened the election of a homosexual bishop in California to "a terrorist bomb, which is timed to destroy a peace process."

The selection of any one of the three "would precipitate some kind of response from the leaders of the Anglican Communion," said the Rev. Ian Douglas, a professor at Episcopal Divinity School in Cambridge, Mass., who is active in national Episcopal politics.

"We'd be fooling ourselves if we thought it would not," he said. "As to what kind of response, that's all uncharted territory, but clearly it would precipitate a response at the global level."

But there are other formidable candidates, including Alabama Suffragan Bishop Mark H. Andrus, previously the rector of Emmanuel Episcopal Church in Middleburg, Va. The National Cathedral's Canon Eugene Taylor Sutton, 52, a D.C. native, is also in the running.

The sole black candidate, he is a canon pastor and director of the Center for Prayer and Pilgrimage. Leaders of the 70-million-member Anglican Communion, which is bitterly torn over the 2003 election of homosexual prelate New Hampshire Bishop V. Gene Robinson, have pleaded with Californians not to fuel the ongoing schism.

A report issued April 7 by an Episcopal special commission urged dioceses to use "very considerable caution" in electing another homosexual bishop and proposed a resolution offering "our sincerest apology and repentance" for not consulting with other Anglicans before electing Bishop Robinson.

In February, Archbishop of Canterbury Rowan Williams said Anglicans require the "highest degree of consensus for such a radical change."

And the Windsor Report, a document issued in 2004 by 18 world Anglican leaders, recommended that no more homosexuals be elected bishop until Anglicans can agree on the matter.

Proponents of electing a homosexual bishop point out that the 22 Anglican provinces that have either partially or completely cut ties to the Episcopal Church over the Robinson consecration are not likely to change their minds.

The Rev. James S. Ward, a Marin County, Calif., priest, compared the election to the civil rights movement in an essay in this coming Sunday's issue of Living Church magazine.

"If the outcome on May 6 is the election of a priest in a same-sex relationship, General Convention will be called to an act of ecclesial disobedience, which in the spirit of Martin Luther King Jr., will be the equivalent of a 'direct action campaign,' "

Mr. Ward wrote. "May we be up to the challenge."

The Rev. John Kater, acting dean and president of the Church Divinity School of the Pacific, an Episcopal seminary across the bay in Berkeley, says local Episcopalians are taking the election seriously.

"The diocese of California is very aware of the implications of this election," Mr. Kater said.

"Will that influence how people vote? It's hard to tell. The mood here is not rebellious at all. I've not heard a single person to say, 'I'll vote to thumb my nose at the Anglican Communion.' "

However, conservative Canon Bill Atwood of the Ekklesia Society, an Episcopal aid network based in Carrollton, Texas, predicts that the Californians will "totally ignore the consequences" of their actions.

"I don't think there's any question they'll be compelled to elect a partnered gay," Mr. Atwood said.

"I think they've got a mistaken understanding of issues of justice. Huge portions of the Episcopal Church are theologically adrift.

"I'm not saying there isn't religion, but it's not the historic Christian faith."

--This story is based in part on wire service reports.