By Mary Wisniewski
(Reuters) - The U.S. Presbyterian Church was close on Tuesday to approving a change in the wording of its constitution to include same-sex marriage, a move which threatens to further splinter one of the largest U.S. mainline Protestant denominations.
The 171 regional "presbyteries" or local leadership bodies of the church have been voting on whether to change the wording to call marriage a contract "between a woman and a man" to being "between two people, traditionally a man and a woman."
The definition under debate is contained in the Louisville, Kentucky-based church's "Book of Order," part of its constitution. The change requires a simple majority of 86 votes, and only one more vote is needed, according to the Presbyterian Lay Committee, a conservative group which opposes the change. The vote could come by Tuesday night.
The church has more than 1.7 million members.
A gathering of elders and ministers of the church voted last June to allow clergy to perform same-sex weddings. The move gave clergy the choice of whether to preside over same-sex marriages in states where they are legal.
In 2012, the church's General Assembly narrowly voted to reject a proposal to redefine marriage as a union between "two people."
The church, also known as PCUSA, has lost more than 500,000 members over the past decade. Some church leaders have expressed concern that endorsement of same-sex marriage could cause an exodus of parishioners who see it as incompatible with biblical teachings.
"These are indeed difficult days for folks both within the PCUSA and other denominations that have made these same choices in the past," said Carmen Fowler LaBerge, president of the Lay Committee, in a conference call on Tuesday.
Clergy will not be compelled to perform same-sex marriage if the wording is changed.
David Gushee, a professor of Christian ethics at Mercer University in Atlanta, said that as with other denominations like the United Church of Christ that have changed policy on gay and lesbian issues, some congregants will be lost, but others will be gained.
"All across Christianity, we see the dominoes falling of abandoning the historic stigma and rejection of gay people and gay relationships," Gushee said.
The U.S. Supreme Court agreed this year to take up the issue of whether states can ban gay marriage, which is now allowed by 36 states and the District of Columbia.
(Editing by Eric Walsh)