LONDON — The Church of England and Roman Catholic bishops of England and Wales formally objected Tuesday to the government's proposal to permit gay marriages, both asserting that their historic understanding is that marriage is the union of a woman and a man.

Prime Minister David Cameron is backing a proposal to permit civil marriages for gay couples, despite the strong opposition of some lawmakers in his Conservative Party. Gay couples are already allowed to have civil partnerships, with the first such ceremony in 2005.

The churches' responses were released on the day when the traditional marriage group Coalition for Marriage delivered a petition with more than half a million signatures to Cameron's office, opposing the change. Thursday is the deadline for public comment, which the government will consider in drafting legislation.

"The uniqueness of the institution of marriage is based on the fact that the human person exists as both male and female and that their union for the purpose of procreation, mutual support and love has, over the centuries of human history, formed a stable unit which we call the family," the Catholic bishops argued.

Home Secretary Theresa May said the government didn't want to impose anything on any religious organization. "We won't be asking anybody to do anything that does against their conscience," said May, whose department is leading the consultation.

With attendance continuing to fall, the Church of England's influence has waned. Perhaps mindful of that, much of the Church of England's criticism of gay marriage focused on legal issues rather than quoting scripture. The response from the church's bishops and the Archbishops' Council argued that gay couples already have many of the legal benefits of marriage through civil partnerships and worried that churches could ultimately be required to perform same-sex marriages.

"To change the nature of marriage for everyone will be divisive and deliver no obvious legal gain given the rights already conferred by civil partnerships," the church said. "We believe that imposing for essentially ideological reasons a new meaning on a term as familiar and fundamental as marriage would be deeply unwise."

Gay marriage backers pointed out that the legislation would only focus on civil marriages and would exempt religious groups from any duty to perform same-sex marriages.

Peter Tatchell, a leader of the Equal Love campaign for gay marriage, accused the church of "scaremongering, exaggerating the effects of same-sex marriage and advocating legal discrimination."

Ben Summerskill, chief executive of the gay rights organization Stonewall, said "many bishops in the Church of England today will be rather pleased because once again they are not talking about global poverty or the HIV pandemic, they are talking about the subject that obsesses them, and that is sex."

The Church of England's traditional stance on marriage contrasts with its evolving attitude toward gender. It has admitted women to the priesthood, and is embroiled in a contentious debate about allowing women to serve as bishops.

About a fourth of weddings in England take place in Church of England churches, which are legally obligated to provide a marriage service for any resident of a local parish who wishes it, regardless of church membership.

The issue has caused friction between Cameron, who is allowing party members to vote their conscience on the legislation, and Deputy Prime Minister Nick Clegg, who expects all members of his Liberal Democrat party to support the change.

Cameron told his party conference in October that the issue was about equality and commitment.

"Conservatives believe in the ties that bind us; that society is stronger when we make vows to each other and support each other. So I don't support gay marriage despite being a Conservative. I support gay marriage because I'm a Conservative," Cameron said.

The Catholic bishops accused the government of moving hastily on the issue "based only on two very brief party conference announcements."

"This proposal, which has the potential to impact so immensely on the social stability of our society and which has significant implications for the unique institution of marriage and of family life, appears not to have been subject to such careful study and analysis," the Catholic bishops said.

The Muslim Council of Britain has joined the opposition. Its Muslims Defending Marriage Campaign asserts that "our creator, Allah, has elevated this institution and conferred upon it blessings unique to it alone."

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