The plan will be presented to the cabinet of President François Hollande, who had made the issue one of his main electoral planks. Hollande has promised that the legislation will be on the statute books by mid-2013.
The liberal cornerstone of Hollande's election manifesto has come under fire in a country which is officially secular but predominantly Catholic.
Muslim, Buddhist, Protestant and Jewish organisations have also signalled their opposition to the project in various ways.
Paris Cardinal André Vingt-Trois, who has led opposition to the project, told mass-goers in the southern pilgrimage town of Lourdes last weekend that children needed both a father and a mother to build their identities.
"When we defend the right of children to build their personality with reference to the man and the woman who gave them life, we are not defending a particular position," he said.
A number of European nations allow gay marriage and adoption, but not France, where only married couples and not civil union partners can adopt.
Belgium, Britain, Denmark, Finland, Germany, Iceland, The Netherlands, Norway, Spain and Sweden currently allow gay adoption.
Polls suggest that up to two-thirds of French voters back homosexuals' right to marry, but they are split on allowing them to adopt.
However opponents say public opinion on gay adoption is waning, citing a recent Ifop poll in which 48 percent said they favoured it against 53 percent in August.
Marine Le Pen, leader of the far-right National Front, has called for a popular vote on gay marriage and adoption.
Jean-Francois Copé, one of two candidates to succeed former president Nicolas Sarkozy as the head of the conservative UMP party, has urged the government to postpone the draft bill saying it was "incredibly badly prepared.
"It is not just about homosexual marriage, it is about a complete reorganisation, deconstruction of the right of the family, with questions surrounding lineage, the removal of the reference to father and mother in the text," Copé said.
Some conservative and far-right politicians have also called for mass street protests to try and force the government to back down. Hundreds of French mayors or deputy mayors have signed a petition opposing the
Pope Benedict XVI last month urged French bishops to oppose the bill and
defend marriage as the "foundation of social life".
But Prime Minister Jean-Marc Ayrault has insisted there will be no
The text to be presented to Hollande's cabinet will redefine marriage to
stipulate that it is "contracted between two persons of different sex or of
the same sex," Ayrault told AFP last month.
The draft legislation will include a provision for married gay couples to
adopt children but the right will not be immediately extended to unmarried
homosexuals, the premier added.
That question and the issue of gay couples' access to medically assisted
conception will be addressed in secondary legislation at a later date.