The country's ruling conservatives and left-wing opposition approved the deal over a controversial draft law on Thursday before a formal vote by the National Assembly next week.
The Socialists said their backing depended on an amendment requiring the law to be reviewed after a year.
Their support also hinged on the understanding that the law would not be wielded in a way that would alienate religious communities.
The head of the Socialists in parliament, Jean-Marc Ayrault, said a law upholding France's principle of secularism should be "a law of national harmony, of republican harmony, and not a law that will divide".
The amendments were seen as a way to bring those hesitating on board to back the bill, which goes to the vote in the lower chamber of parliament next Tuesday. It will then be passed to the upper chamber, the Senate.
A Socialist lawmaker, Rene Dosiere, said the deal with Chirac's ruling Union for a Popular Majority meant "the text will be improved enough so that the Socialist group can vote for it".
Chirac says the law will uphold
French public opinion backs the idea of a ban on conspicuous religious insignia in state schools, as does President Jacques Chirac and some key ministers.
The bill, approved by the government a week ago, says that in state schools "the wearing of signs or clothes which conspicuously display a pupil's religious affiliation is prohibited".
It would apply also to Jewish skullcaps, large Christian crosses and the Sikh turban.
But others are reluctant to legislate on the matter, especially after protests by many of France's estimated five million Muslims, and by members of the 6000-strong Sikh community.