David Cameron wants churches in England and Wales to be allowed to conduct same-sex marriage ceremonies.
He said he did not want gay people to be “excluded from a great institution”, but would not force any groups to hold ceremonies in their places of worship.
Ministers will reveal their response to a consultation next week. MPs will be given a free vote on the issue.
The Church of England said it would study the proposals but was firmly against same-sex marriage.
In a statement, the Church said: “We believe that redefining marriage to include same-sex relationships will entail a dilution in the meaning of marriage for everyone by excluding the fundamental complementarity of men and women from the social and legal definition of marriage.
“Given the absence of any manifesto commitment for these proposals – and the absence of any commitment in the most recent Queen’s Speech – there will need to be an overwhelming mandate from the consultation to move forward with these proposals and make them a legislative priority.”
The Church said its stance was not a “knee-jerk resistance to change”, but was “motivated by a concern for the good of all in society”.
Mr Cameron’s proposals have also angered some Tory MPs who have opposed the change in the law.
Bob Blackman, MP for Harrow East, warned there will be “outrage throughout the country” and a “clear backlash” against David Cameron’s proposals.
He told BBC News: “Marriage is between one man and one woman and so changes to the definition of marriage are not appreciated and not strongly supported.”
He said he was against teachers “being forced to say same sex relationships are the equivalent of heterosexual relationships” – something he said would happen if the move become law.
Labour and the Lib Dems have yet to decide whether to join the Conservatives in granting their MPs a free vote on the issue, although the majority of MPs in the three parties are thought likely to back it.
But Mr Blackman predicted the legislation could face “an interesting challenge” in the House of Lords.