AULNAY-SOUS-BOIS, FRANCE - The fire engine and police sirens blaring through the darkness Wednesday night, as officers raced to put out yet another fire set by angry youths in this poor Paris suburb, signaled more than an immediate warning of danger. After a week of nightly disturbances that have left hundreds of cars and buses torched, and several buildings burned down, the horns echoing off the concrete walls of grim housing projects sounded a broader alarm. The spreading violence has lifted the lid on an ugly stew of poverty, discrimination, and desperation amongst immigrant-descended families that most French citizens have long preferred to ignore. "Frankly I am not surprised by what is happening," says Dounia Bouzar, an expert on French-born Muslims who has worked in the mostly black and North African districts on the outskirts of Paris. "Given the way these kids live, I wonder why it doesn't happen more often." The outburst of violence, pitting youths throwing stones and Molotov cocktails against riot police, erupted after two teenagers in the nearby suburb of Clichy-sous-Bois - apparently hiding from the police - died by electrocution. That incident, says social worker Michèle Lereste, "crystallized the hatred" that some of the most disaffected and hopeless young men living in what the government calls "sensitive urban zones" feel toward authority. In these 751 zones that the government has designated for special programs, unemployment stands at 19.6 percent - double the national average - and at more than 30 percent among 21- to 29- year-olds, according to official figures. Incomes are 75 percent below the average. Stung by charges that the government has mishandled the wave of unrest in a dozen suburbs, Prime Minister Dominique de Villepin and Interior Minister Nicolas Sarkozy have both cancelled planned trips abroad. President Jacques Chirac called Wednesday for "dialogue" to cool tempers. Mr. De Villepin and Mr. Sarkozy met Thursday to discuss ways of dampening the violence beyond deploying more riot police, which has been the government's approach so far. But after two decades of policies that have tried, and often failed, to strengthen schools, provide jobs, and improve housing, critics say it is time authorities took the problems more seriously. The ugly, often poorly maintained blocks of public housing that have become a nightly battlefield are testament to 40 years of government policy that has concentrated immigrants and their families in well-defined districts away from city centers, as housing there became more expensive. "Working class suburbs have become ethnic ghettos," says Marc Cheb Sun, who edits "Respect," a magazine aimed mostly at young black and North African readers. "That is the origin of the problem." And it is not easy for even ambitious young people to break out if they come from a district with a bad reputation, as Jean-Francois Amadieu, a university professor who founded the "Discrimination Observatory" discovered in experiments over the past year. He sent out fictitious applications for sales jobs, allegedly coming from six different sorts of applicant, ranging from a white male to a woman of North African origins, all with the same résumé. Applicants writing from addresses known to be in "difficult" areas received half as many invitations to an interview as those from less notorious districts. The "North African" male candidate received five times fewer invitations than his white counterpart, says Prof. Amadieu. At the same time, complains Michèle Lereste, who runs the "Green Light" social-work agency in Villetaneuse, just North of Paris, where the projects are almost entirely inhabited by immigrant-descended families, government funding cuts have closed a number of job-training institutes, "and we are finding it harder and harder to get employers to take apprentices from our district." "The kids learn all the French republican values such as equality in school, and then they find in practice that it's an illusion," says Ms. Bouzar, who was recently named one of Time magazine's 50 "European Heroes" as a role model for those seeking to be good Muslims and good French citizens. "There is an enormous gap between theory and practice." Nowhere is that gap clearer, say young men in Clichy-sous-Bois and adults who work with them, than in the behavior of the police. "They check our papers everywhere, all the time, for no reason," complains one youth in Clichy who did not want to be identified. "And the checks are getting rougher and rougher." Those sorts of experiences "delegitimize the state" in young peoples' eyes, worries Bouzar, which helps explain why authority figures such as firemen and doctors have been stoned on recent nights even as they tried - with police protection - to save lives and property. Taïb Ben Thabet, who has been a social worker in the projects north of Paris for 35 years, fears that the kind of discrimination his young wards face undermines his patient efforts to help them find their place in society. "I teach them that the state is for everybody, that it treats everybody the same," he says. "But what credibility do I have when everything I say is contradicted by experience? The kids say it's all lies." He is particularly upset by the manner in which Mr. Sarkozy referred to youths in the projects recently as "scum," pledging a "war without mercy" against them. "We are giving power to the (Islamic) radicals," he argues. "When kids hear the minister call them scum, the obscurantists are there to take advantage of the way they feel." "This is not just a problem for the kids in the projects," warns Mr. Cheb Sun. "Society created these ghettos and now it has to deal with them."