France is an idea, says the Gaullist intellectual Philippe Seguin. On the streets of Grigny in the Paris suburbs these days, it looks like the wrong idea.

At the entrance to La Grande Borne estate the remains of a burnt-out car blocked the road and broken glass littered the pavement. A group of youths huddled together, discussing the previous evening's clash with the police, which left two officers with gunshot wounds. One youth - a scar down his cheek and the nose of a boxer - turned sharply in response to a question. "Get out of here," he snarled.

A second agreed to talk in a car park a few hundred metres away. Abdelsalam, 17, was typical of the rioters who have burnt more than 5,000 vehicles and 200 public buildings in France's worst urban violence since 1968.

The son of parents who came from Algeria in the 1970s, he left school at 16 without qualifications and has been looking for a job ever since. "When employers see I've got a North African name and that I live in La Grande Borne, the vacancy disappears. I spend my days hanging around here with my friends. There's nothing to do, so you can't blame us for burning cars."

His only regular contact with mainstream France is the police. "They're always stopping me and they're always aggressive. I say 'Bonjour monsieur' and they answer by calling us pigs and telling us to go back into our holes. The other day, one of them called my mother a whore. How can you accept that? I'm telling you: it's war between us and them."

His words are depressingly familiar. For 30 years les beurs (the children of North African immigrants) have complained about discrimination, exclusion and harassment, and for 30 years the authorities have promised to help them. Jacques Chirac, for instance, was elected president in 1995 on a pledge to end la fracture sociale. But Chirac has failed, and now he seems at a loss as to how to respond.

One reason for this is that his policies are shaped by a philosophy, articulated by the likes of Seguin, which holds that France cannot be defined geographically, genetically or historically. It is not a lump of land, nor a people, nor even the accumulation of centuries of demographic movements, kingdoms, wars, revolts, disasters and triumphs.

Instead, France is a political ideal that emerged after the revolution, an ideal of democracy, human rights and equality which is upheld by a public education network that offers the same chance to all.

There is no place for race, creed or colour in this system, and therefore no tools for dealing with the issues behind Abdelsalam's bitterness.

France, for example, has no statistics on the (pitifully small) number of ethnic-minority police officers, or judges, or managers in big business, because that would introduce a notion of division between its citizens. In Seguin's vision, the mere suggestion of race or religion is an attack on the essence of French identity.

But is there any option? "I know that things go wrong in Britain, too," said Abdul Mzi, an education worker in Grigny. "But at least you have doctors and lawyers from the ethnic minorities - at least they have some chance of moving up the social ladder. Here, all the doors are shut. The politicians talk about integration through school and work, and that may have functioned for Italian, Polish, Spanish and Portuguese immigrants in the 20th century. But it just hasn't worked for African and North African immigrants. They are stuck here in council estates in the suburbs and everyone forgets about them except when they riot. We've got to accept that the system is failing them and we've got to try something else."

One of the few politicians to share this view, paradoxically, is the interior minister, Nicolas Sarkozy, a hate figure to rioters since he pledged to clean their estates of "scum". Sarkozy has broken a taboo by calling for affirmative action to help minorities.

Though Chirac slapped him down, this debate will continue long after the riots have ended. The central question for voters in the 2007 presidential election may yet be: can France continue to shun multiculturalism in the name of its republican ideal?