The call to arms has been circulating on French blogs and text messages for days: "All the housing projects should rise. The wait is over. Friday, Nov. 11, a meeting under the Eiffel Tower. At 2 p.m. Show up, it's important."

"We are aware of it and we're taking this very seriously," said one Paris police official, who asked that his name not be used because of a national police edict prohibiting local police authorities from discussing the crisis with the news media. He added of the war cry, "We don't quite know what to make of it."

While riot police are attempting to curb the gangs that have been setting fire to cars and buildings in France's poor suburban communities for the past two weeks, French officials have only just begun the struggle to control a more amorphous battleground: cyberspace.

Internet blogs have become so vicious and intense that police have opened investigations against two teenagers for inciting violence on radio station-sponsored blogs. Hackers took over the Web site of the northern Paris suburb of Clichy-sous-Bois, where the first violence began Oct. 27, and dispatched thousands of fake e-mails announcing the mayor's resignation. Local gangs have used text messaging on their cell phones as early warning systems to alert members about the movements of riot police during operations in their communities, gang members said in interviews.

"It is the first time France has experienced a real crisis in the age of the Internet," said Bruno Patino, co-author of a newly published book, "The Press without Gutenberg," about the Internet's emerging dominance over traditional media outlets. "And it's easy to see how the Internet can increase the momentum of the crisis."

French law enforcement officials say they are investigating possible use of the Internet for coordinating attacks among some of the 300 cities across the nation where the violence has spread like an epidemic. But Web monitors and sponsors said the greatest impact of the Internet has been as a forum conveying messages that incite further violence.

"The comments are very, very violent on both sides -- by the people who are calling for the rioting and the people who are anti-riot and are very radical in their ideas," said Stephane Dreyfus, a member of the Web team at France's daily La Croix newspaper. "We find it quite worrying."

The Web site of Skyrock, a French radio station popular among young people, shut down its most provocative blogs this week after the exchanges became increasingly vile and bloggers used the forum to call for a violent gathering at the Eiffel Tower on Friday. According to police, other bloggers have urged an assembly Saturday on the Champs-Elysee, France's most famous boulevard.

"God bless France, because war is about to begin," wrote a blogger called Nour.

"The hate will turn around," countered another who signed his name as Raslebo. "I am sick of these bearded fascists."

In recent days, the tone and description of the crisis on the Internet has started to diverge dramatically from the version on television and in the traditional news media. The Internet was being flooded with messages inciting violence Wednesday as the country's largest television network announced that it would no longer report the number of burned cars, in an effort to cool the competition between gangs.

Figures released by the national police indicate that the number of vehicle arsons has declined and that the violence has subsided in some areas, including the northern suburbs of Paris where the rioting was set off by the electrocution of two teenagers who hid in a power substation to avoid potential harassment at a police checkpoint. The Interior Ministry said 617 cars were burned Tuesday night compared with 1,100 the previous night. Incidents were reported in 116 towns, compared with 226 the night before, it reported. Although the government has imposed a state of emergency that allows local officials to impose curfews, only a handful of cities have done so, including Nice and Cannes on the Mediterranean coast.

Violence continued unabated in many cities Wednesday night. Vandals set fire to a kindergarten near the center of the Reynerie subdistrict in the Toulouse suburb of Mirail. Unlike on previous nights of unrest in the neighborhood, however, the young men roaming the streets did not wait for the arrival of police officers to take action.

At exactly 6 p.m., a small white car zoomed through the parking lot of a high-rise apartment block to the cheers of a clutch of young men idling nearby. The car pulled up to the state-run school, and a masked man emerged and tossed a firebomb into the entryway of the single-story building. It went up quickly in hissing flames.

Police officers arrived 20 minutes later to escort firefighters to the site, but the building was already heavily damaged. There was no visible attempt to arrest or question anyone about the incident. A helicopter circled overhead shining a spotlight on the streets and alleyways.

Interior Minister Nicolas Sarkozy announced Wednesday that any immigrants convicted of participating in the riots would be deported, even those who are legally resident with visas. The majority of youths involved in the rampages, however, appear to be the French-born children of immigrant parents.

Police also have increased their monitoring of Web sites and blogs, authorities said Wednesday. A 16-year-old French youth and an 18-year-old Ghanaian from the northern Paris suburbs are under judicial investigation for "provoking willful property damage that posed a danger to people via the Internet," prosecutors said. A 14-year-old from the southeastern city of Aix-en-Provence was also questioned, but has been released without charges, according to authorities.

Although the youths did not know one another, each had posted blogs on Skyrock radio's Web site.

One of the blog notices urged, "Go to the nearest police station and burn it," according to authorities.

Skyrock officials said they would make no comment on the police action or their decision to close the most provocative blogs.

In an interview last weekend, the radio station's president, Pierre Bellanger, said the station, which was receiving up to 20,000 blog comments a day, "can't accept having calls to violence, blogs saying 'I want to kill the cops.' " He said a team of 30 monitors and filtering software helped ensure that violent notices were not posted.

But other Web site directors said the volume of comments funneled into the Skyrock blogs became too voluminous to control.

"Blogs are difficult to monitor," said Fabrice Rousselot, deputy editor of the newspaper Liberation's Web site. He said the site has determined it is "too risky" to have open blogs. Web monitors even have trouble controlling the comments posted in forums, he said, adding that some of the more outrageous messages can remain posted for several minutes before monitors are able to suppress them.

But many of the blog postings inciting violence were balanced against calls for halting it. One of Skyblog's writers noted, "It's a great idea, this meeting around the Eiffel Tower Friday. But we have to be calm, if not all of this will come to nothing. We have things to say, all the media will be there and no one will stop us."

Williams reported from Toulouse.

A fireman confronts a burning car in Toulouse. Riots have spread from suburbs of Paris to 300 French cities since Oct. 27.