The key innovation of the bill is a contract called the Civil Solidarity Pact (PACS) open to cohabiting heterosexual and homosexual couples - and in some cases brothers and sisters.

The PACS would extend some of the financial advantages that go with marriage to non-married couples, allowing them, among other things, to file joint tax returns, gain inheritance benefits, and take part in the other's social security coverage.

The gay rights movement has kept up the pressure

Conservative opponents of the reform say it will undermine Christian family values, pave the way for gay marriage and adoption of children by homosexual couples. They have tabled more than 1,000 amendments.

On Tuesday night, one of the bill's most outspoken opponents, Christine Boutin, member of the Union for French Democracy, spoke for more than five hours against the bill.

The ruling left-wing coalition defeated by 299 votes to 233 the conservatives, who wanted the PACS rejected out of hand.

Debate on the bill, which was stopped three weeks ago after the opposition voted out the first draft, will continue on Saturday.

Government embarrassment

The first reading of this bill was a moment of rare embarrassment for the socialist government of Prime Minister Lionel Jospin.

He had promised gays a law to enhance their position in society, but not enough socialist MPs bothered to turn up to the debate and the opposition overturned the bill on a technicality.

This time, the government has been determined not to make the same mistake and officials have been busy marshalling deputies into line.

Left-wingers say the PACS is needed to adapt outdated laws to the evolution of French society, where marriages are on the decline and many young couples do not bother to go to church or the registrar's office to seal their relationship.

"Want to pacs with me?"

But the bill has sparked a furious debate in the once deeply Roman Catholic country.

Bishops have condemned it as "useless and dangerous". Groups of Christians have been praying in churches and convents for the bill to be defeated.

Posters in Paris metro stations warn of an end to the family.

But correspondents say the word PACS has already become part of the popular language, with young people jokingly asking each other: "Do you want to pacs with me?"