Five high-speed trains, 900 buses and countless car pools left provincial towns, many before dawn, and headed toward three starting points in the capital for the marches due to converge at the Eiffel Tower in the late afternoon.

Strongly backed by the Catholic hierarchy, lay activists have mobilised a hybrid coalition of church-going families, political conservatives, Muslims, evangelicals and even homosexuals opposed to gay marriage for the show of force.

"We want this draft law to be withdrawn," Patricia Soullier, a protest organiser, told BFM-TV before boarding a Paris-bound train in Montpellier in the south of France.

Several hundred thousand were expected to march in near freezing temperatures against the reform, which Hollande promised in his election campaign and has enough votes in parliament to pass easily.

The president angered many opponents by trying to slip the reform through parliament without much public debate and has wavered about some details of the reform.

His clumsy handling of other promises, such as a 75 percent tax on the rich that was ruled unconstitutional or his faltering struggle against rising unemployment, has soured the public mood. A mass street protest can hardly help his image.

Frigide Barjot, an eccentric comedian leading the so-called "Demo for All", insists the protest is pro-marriage rather than anti-gay and has banned all but its approved banners saying a child needs a father and a mother to develop properly.

Same-sex nuptials are legal in 11 countries including Belgium, Portugal, Netherlands, Spain, Sweden, Norway and South Africa, as well as nine U.S. states and Washington D.C.

CHILDREN

Cardinal Andre Vingt-Trois, head of the Catholic Church in France, spearheaded the opposition with a critical sermon in August. Other faith leaders - Muslim, Jewish, Protestant and Orthodox Christian - soon spoke out too.

They struck a chord with voters by stressing problems for children that they saw emerging from same-sex marriage rather than using purely religious arguments against it or letting the government shape the issue of one only of equal rights for gays.

Support for gay nuptials has slipped about 10 points to under 55 percent and fewer than half the French now want homosexuals to win adoption rights.

Under this pressure, legislators dropped a plan to also allow lesbians access to artificial insemination, which is now limited to heterosexual couples with fertility problems.

Organisers insist they are not against gays and lesbians, but for traditional marriage. "We are marriagophile, not homophobe," said Barjot, author of a book entitled "Confessions of a Trendy Catholic".

Most national faith leaders will not join the protest, but at least eight Catholic bishops have said they would march.

"I'm happy many Catholics will be mobilised, but this is not a church demonstration against the government," said Vingt-Trois, who plans to go meet marchers but not join them.

Opposition leader Jean-Francois Cope and other conservatives, as well as leaders from the far-right National Front, will march as private citizens without political banners.

Civitas, a far-right Catholic group whose protests have been openly anti-gay, plans a rival march that will run parallel to one of the "Demo for All" columns. Organisers say they will have about 10,000 volunteer marshals to keep order.