MOSCOW, January 14 (RIA Novosti) - Hundreds of thousands of people on Sunday marched through the streets of the French capital Paris to protest President Francois Hollande’s plans to legalize gay marriages and adoptions by June, media reported.

According to the British broadcaster BBC, three big marches converged on a large park next to the Eiffel Tower - the Champs de Mars.

The demonstrators, who are supported by the Catholic Church and the right-wing opposition, say the authorities' plans would undermine one of society’s essential building blocks.

France allows civil unions between same-sex couples, but during his presidential campaign, Hollande pledged to extend their rights. Although his socialist government faced opposition from over 1,000 mayors and the Catholic Church, it still approved a relevant bill in November 2012.

The march organizers said some 800,000 protesters took to the streets, carrying placards that in particular read, "We don't want your law, Francois." According to police, the number of protesters was about 340,000.

The French parliament is expected to start discussing the controversial legislation later in January. Paris-based news channel France 24 reported citing recent opinion polls that over 60 percent of people surveyed support marriage rights for same-sex couples.

Catholic leader Cardinal André Vingt-Trois, who launched the opposition with a critical sermon in August, met protesters in south Paris to express his "encouragement that Christians express what they think,” according to the Sky News satellite television news broadcaster.

Sky News also said organizers insisted they are for traditional marriage rather than against gays and lesbians.

In November 2012, between 70,000 and 200,000 of French nationals protested the French authorities’ plans to legalize same-sex marriage and allow gay couples to adopt, media said. Catholic groups and other supporters of traditional family rights were among the participants.

Updated with parliament debate date, opinion poll data.