The Anglican Church is bracing itself for more confrontation over homosexual clergy as California's Episcopal Church meets to choose a new bishop.
Three of the seven candidates in Saturday's election are gay.
The Archbishop of Canterbury has expressed unease over the nominations, which correspondents say could push the Anglican Church closer to a split.
The election of openly gay priest Gene Robinson as Bishop of New Hampshire three years ago caused great division.
A majority vote for the Reverend Bonnie Perry, from Chicago, would make her the first lesbian bishop in the church.
The other gay candidates are Canon Michael Barlowe, who works in the Diocese of California, and the Very Rev Robert Taylor of Seattle.
The other candidates are Right Rev Mark Handley Andrus of Alabama, the Rev Jane Gould of Massachusetts, the Rev Donald Schell of San Francisco and the Rev Canon Eugene Taylor Sutton, canon pastor of Washington National Cathedral.
Martin Reynolds, from the Gay and Lesbian Christian Movement, said the decision could have a significant impact, yet the nominees had been chosen after extensive searching - and he believed their sexual orientation should not matter.
"The actual front-runner is a woman who's a lesbian - she's living with her partner - and it looks like she's the front runner because she's trebled the congregation size in her church in a very short period of time," he told the BBC.
"She's got people there from all parts of the community - the very young, very elderly - she seems to be the front-runner because she's a very effective evangelist."
Seven-hundred priests and lay people will gather at Grace Cathedral in San Francisco for the election, which is being watched not only by the Archbishop of Canterbury Dr Rowan Williams, but by Anglicans worldwide.
The issue of gay clergy is splintering the Anglican Church.
A number of Anglican provinces have already broken with the American church, which they believe is pursuing a liberal, unbiblical agenda.
The Californian election has to be ratified at the US Church's general convention next month.
Some bishops have already suggested they would block the consecration of a second homosexual bishop in order to preserve the fragile unity of the Church, the BBC's Jane Little in Washington says.
