France's new Socialist government is to legalise marriage and adoption for same-sex couples, Prime Minister Jean-Marc Ayrault said on Friday, reflecting a shift in public attitudes in the majority Catholic nation.

President Francois Hollande, who took office on May, had pledged to legalise gay marriage and adoption during his election campaign but had given no time frame.

Since Hollande's Socialists won an absolute majority in parliamentary elections two weeks ago, the conservative UMP party, which had opposed the measure under former president Nicolas Sarkozy, can do little to stop it.

"The government has made it an objective for the next few months to work on implementing its campaign commitments on the fight against discrimination on grounds of sexual orientation and gender identity," Ayrault's office said in a statement.

Earlier in the day, the junior minister for families Dominique Bertinotti told French daily Le Parisien that a law on gay marriage and adoption would be passed within a year.

The statement from Prime Minister's office did not confirm the time frame, but asserted a law would be implemented.

In addition, the government would hold discussions in the autumn on ways of making life easier for trans gender individuals, whose dealings with French administration are often complicated by their change of name and sex.

A law granting full marriage status to gay couples would bring France, which currently provides only for same-sex civil unions, into line with fellow EU members Denmark, Portugal, Spain, Belgium, the Netherlands and Sweden.

It would also mark a profound change in French society, where more than two-thirds of people still describe themselves as Roman Catholic, according to a 2010 survey by pollster Ifop.

However, fewer and fewer of them adhere to strict Roman Catholic teachings on sexual issues or back the Vatican's condemnation of homosexuality. Church attendance has collapsed.

As recently as 2006, surveys indicated that most French were opposed to changing the definition of marriage, but now more than 60 percent support the idea, the pollster BVA said. A majority also favour allowing gay couples to adopt children.

Nevertheless, gay rights advocates say homosexuality remains taboo in many areas of public life. Media tend to use euphemisms such as ‘long-term bachelor’ to hint that someone is gay.

"Today, it's still very difficult to put a name on things, as if saying in public that someone was homosexual was to violate a taboo," a group of gay professionals wrote in an opinion piece in the newspaper Le Monde on Friday, the eve of a Gay Pride march in Paris.

A gay marriage law would boost Hollande's credentials as an agent of social change in the tradition of late Socialist president Francois Mitterrand, who appointed France's first female prime minister and scrapped the death penalty.

Hollande fathered four children out of wedlock with his former partner, fellow Socialist Segolene Royal.

A debate on gay rights might also draw some attention away from the economic woes weighing on his popularity.

Still, there is certain to be opposition from conservatives and practising Catholics.

"We are convinced that young people's development requires the presence of a mother and a father," said Thierry Vidor, head of the Familles de France umbrella group, which represents some 70,000 families, and campaigns for traditional family rights.

"We will take action to try to show that this measure is ultimately dangerous for society."