The US Episcopal Church is poised to become the first major religious denomination in the United States to approve a rite for blessing gay marriages after its bishops overwhelmingly approved such a liturgy on Monday.

The proposed blessing was agreed by the church's Chamber of Bishops at a meeting in Indianapolis and is expected to receive final approval from its House of Deputies later this week, Ruth Meyers, a chair of the Episcopalians' Subcommittee on Prayer Book, Liturgy and Church Music, told Reuters.

The decision would go into effect in December and make the Episcopal Church, an independent US-based institution affiliated with global Anglicanism, the biggest US church to allow a liturgy for same-sex marriages.

The Episcopal Church is the 14th-largest denomination in the United States with nearly two million adherents, according to the National Council of Churches.

The United Church of Christ, a mainstream Protestant denomination with about a million members, has gone further so far than any other US church, voting in 2005 to support same sex marriage.

The new Episcopal same-sex liturgy, called "the Witnessing and Blessing of a Lifelong Covenant," would be a standard rite for same-sex marriage.

For the past three years, bishops have been able approve requests for the blessing of same-sex marriages and Jeffrey Lee, the Bishop of Chicago, said he had authorized such ceremonies using an earlier version of the liturgy.

Resistance to similar measures in the past has been strongest among bishops, but Monday's vote was 111 in favor to 41 opposed with three abstentions.

The convention also approved inclusion of transgender people among those who should not be discriminated against, either for ordination or as lay leaders.

"Today the Episcopal Church affirmed the human dignity of a deeply stigmatized population that is far too often victim to discrimination, bullying and abuse," the Reverend Lowell Grisham, a leader of the Chicago Consultation, a group that supports equality, said in a statement.

The Episcopal Church allowed gay priests 16 years ago and approved its first openly gay bishop nine years ago.

The decision by the bishops is the latest in a string of victories for gay-rights advocates in the United States. Gay marriage is legal in six states and the District of Columbia.

The legislatures of three states - New Jersey, Maryland and Washington state - approved gay marriage this year, although New Jersey Governor Chris Christie vetoed it. Governors in the other two states signed the legislation but there are efforts to block it by referendum.

President Barack Obama endorsed gay marriage in May.

On Friday, the Presbyterian Church, the 10th-ranked US denomination, narrowly rejected a proposal to redefine marriage as a union between a man and a woman.

The global Anglican Communion groups independent national churches, which develop their own rules for ordination and other matters pertaining to membership and conduct.

- Reuters