But the 2009 convention had encouraged bishops in states allowing same-sex marriage - currently six, and the District of Columbia - to "provide generous pastoral response" to gay and lesbian members. It also authorized creation of the rite now under consideration.
Its passage would be a major advance for gay people within the two-million-member denomination, says Bishop Charles E. Bennison Jr. of the Diocese of Pennsylvania.
He serves on the legislative committee that will present the measure to the 300-member House of Bishops and the 800 laity and clergy who make up the House of Deputies. If the same-sex blessing is to pass, both houses must approve it.
"For some people, it's going to be troubling. For others, it's going to be thrilling," said Bennison, whose 55,000-member diocese encompasses Philadelphia and the four suburban counties.
The measure seems to have broad support in the House of Deputies, he said. But some moderate bishops, he added, fear it could divide their dioceses. A hearing on the blessing is set for Saturday evening, but a vote is not yet scheduled.
Despite growing public acceptance of gay rights, homosexuality remains a contentious topic for mainline Protestant churches. In May, the General Conference of the United Methodist Church soundly rejected a measure that would have removed a line from the church's statement of beliefs that homosexuality is "incompatible with Christian teaching," which has been the UMC's explicit position for the past four decades. They did not vote on proposals allowing openly gay clergy or same-sex blessings.
On Monday, a committee of the General Assembly of the Presbyterian Church (USA) debated proposals to change its definition of marriage from "the union of a man and a woman" to "the union of two people," and permit clergy to perform same-gender marriage in states where it is legal.
Even if the Assembly, convened in Pittsburgh, adopts the measures, a majority of the church's 173 regional bodies, or presbyteries, would also have to approve before they become church law.
The proposed Episcopalian rite is similar to the wedding liturgy that its opposite-sex couples use, said the Rev. Ruth Meyers, chairwoman of the church's Standing Commission on Liturgy and Music that devised it.
"But the [same-sex] couple's commitment to one another as being rooted in their commitment to God is more explicitly stated" than in the traditional wedding rite in the church's Book of Common Prayer.
A professor of liturgics at the Episcopal seminary in Berkeley, Calif., Meyers said her commission studied hundreds of home-made and unauthorized blessing rites, some dating to the 1970s, after it issued a public call for them three years ago.
Titled "The Witnessing and Blessing of a Lifelong Covenant," the proposed liturgy also allows for an exchange and blessing of rings that have already been exchanged. "We're aware," Meyers said, "that some people in committed relationships might have given each other rings 20 years ago."
In 2009, the General Convention, which meets triennially, also authorized her commission to develop a theological and cultural basis for blessing same-sex unions.
While acknowledging that Christianity and Judaism have long regarded homosexual relations as sinful, the commission report contends that some of those condemnations are rooted in ambiguous biblical passages.
Paul's condemnation of "unnatural" sex acts in the Book of Romans, they say, might have been a condemnation of temple prostitution. And Leviticus' command that homosexual acts be punished by stoning, while "difficult," can be discounted as a byproduct of the "strict gender hierarchy of the ancient Mediterranean world."
A longtime supporter of a same-sex blessing, Bennison said in a recent interview that he was not entirely certain the measure would win the necessary approval in the House of Bishops.
"Some bishops I've talked to say it's going to be much easier for the deputies" - the laity and clergy who make up the convention's "lower" chamber - "because they don't have to face the fallout," he said. "It's the bishops' desks where the mail is going to land" in dioceses where gay marriage is largely perceived as an assault on Christianity.
However, Bishop Sean Rowe of the Episcopal Diocese of Northwestern Pennsylvania, based in Erie, said passage appeared assured "and unlikely to prove destructive."
Reaction within his "middle-of-the-road" diocese will be "mixed" if it passes, Rowe predicted. "For some it will be a cause to celebrate, and for others a source of disappointment. But we've been having conversations on human sexuality for some time, and learned to disagree in ways that are charitable."
Bennison, who as a seminary professor in the 1990s organized some of the Episcopal Church's earliest seminars on same-sex marriage, said he did not expect passage of the rite to be nearly as controversial as the 2003 ordination of the Rev. Gene V. Robinson as bishop of New Hampshire.
After the New Hampshire diocese elected the openly gay Robinson by a wide margin, the House of Bishops approved the appointment, and the denomination's presiding bishop joined in his consecration.
Robinson's ordination outraged Anglican bishops in Africa, Asia, and South America, however, and provoked nearly half the parishes in the Pittsburgh diocese to quit the Episcopal Church in 2008. They have since formed the Anglican Church in North America, which claim 1,000 conservative congregations and 100,000 members in the United States and Canada.
For Bennison and many other Episcopalians who advocate for gay ordination and marriage rights, however, the biblical injunctions against homosexuality are important - but not the final word.
"We have [biblical] texts that endorsed slavery, but nobody today believes that slavery is the will of God," he said. "So there's continuing revelation" about notions of right and wrong.
"That doesn't mean we can make up anything we want to," he said, "but the authority to accept what scripture means lies in the community of believers."
Contact David O'Reilly
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