DETROIT (AP) -- The top legislative body of the Presbyterian Church (U.S.A.) voted Thursday to redefine Christian marriage in the church constitution as the union of "two people" instead of only "a man and a woman."

The amendment requires approval from a majority of the 172 regional presbyteries, which will vote on the change over the next year. But in a separate vote that will take effect immediately, the Presbyterian General Assembly allowed ministers to preside at gay weddings in states where gay marriage is legal. Nineteen states and the District of Columbia recognize same-sex marriage.

The votes at the Detroit event were a full victory for Presbyterian gay-rights advocates. In 2011, the Presbyterian Church (U.S.A.) had eliminated barriers to ordaining clergy with same-sex partners, but did not recognize gay marriage.

Alex McNeill, executive director of More Light Presbyterians, a gay advocacy group, said the decisions Thursday were "an answer to many prayers" of same-sex couples.

"We will keep praying that the majority of our 172 presbyteries will confirm that all loving couples can turn to their churches when they are ready to be married," McNeill said.

Since the 2011 vote on gay ordination, 428 of the denomination's more than 10,000 churches have left for other more conservative denominations or have dissolved. The church now has about 1.8 million members. Still, some theological conservatives have remained within the denomination as they decide how to move forward. The conservative Presbyterian Lay Committee decried the votes in Detroit as an "abomination."

"The General Assembly has committed an express repudiation of the Bible, the mutually agreed upon Confessions of the PCUSA, thousands of years of faithfulness to God's clear commands and the denominational ordination vows of each concurring commissioner," the committee said in a statement.

Of the mainline Protestant denominations, only the United Church of Christ supports gay marriage outright. The Episcopal Church has approved a prayer service for blessing same-sex unions. The Evangelical Lutheran Church in America has eliminated barriers for gay clergy but allows regional and local church officials to decide their own policies on ordination.

The largest mainline group, the United Methodist Church, with about 7.8 million U.S. members, bars ordaining people in same-sex relationships. However, church members have been debating whether to split over their different views of the Bible and marriage, because gay marriage supporters have been recruiting clergy to openly officiate at same-sex ceremonies in protest of church policy.

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Zoll reported from New York.