A French high school philosophy teacher and author who carried out a scathing attack against the Prophet Muhammad and Islam in a newspaper commentary says he has gone into hiding under police protection after receiving a series of death threats, including one disseminated on an online radical Islamist forum.
The teacher, Robert Redeker, 52, wrote in the center-right daily Le Figaro 10 days ago that Muhammad was ''a merciless warlord, a looter, a mass-murderer of Jews and a polygamist,'' and called the Koran ''a book of incredible violence.''
The Redeker case is the latest manifestation in Europe of a mounting ideological battle that pits those who believe Islam and the Prophet Muhammad can be criticized in the name of free speech against those in the Muslim community who believe no criticism can be tolerated.
A recent speech by Pope Benedict XVI that seemed to link Islam and violence caused such an uproar in the Muslim world that the pope issued a rare expression of regret.
The pope expressed regret for the reaction to his remarks after Muslims demonstrated against him around the world. Just this week, a Berlin opera house decided to cancel performances of the Mozart opera ''Idomeneo'' because of security fears over a scene showing the severed head of the Prophet Muhammad. The decision prompted an outpouring of protest about what was seen as the surrender of artistic freedom.
In his commentary, Mr. Redeker compared Islam unfavorably to Christianity and Judaism, although he admitted that the history of the Catholic Church was ''full of dark pages,'' and he criticized the hostile reaction to the pope's remarks.
''Jesus is a master of love; Muhammad is a master of hatred,'' Mr. Redeker wrote, adding, ''Whereas Judaism and Christianity are religions whose rites forsake violence and remove its legitimacy, Islam is a religion that, in its very sacred text, as much as in some of its everyday rites, exalts violence and hatred. Hatred and violence dwell in the very book that educates any Muslim, the Koran.''
Immediately afterward, Mr. Redeker, who teaches in a public high school near Toulouse and is the author of several books on philosophy, began to receive death threats by telephone, e-mail and through the online Islamist Web site known as Al Hesbah, a password-protected forum with ties to Al Qaeda. The forum published photos of him and what it said was his home address, directions to his home and his cellphone number, according to the SITE Institute, which tracks violent Islamist groups.
That day's issue of Le Figaro was banned in Egypt and Tunisia. Mr. Redeker was denounced by a commentator on Al Jazeera television.
''I can't work, I can't come and go and am obliged to hide,'' Mr. Redeker told Europe 1 radio in a telephone interview from an undisclosed location on Friday. ''So in some way, the Islamists have succeeded in punishing me on the territory of the republic as if I were guilty of a crime of opinion.''
Mr. Redeker, who has kept in contact with news agencies by cellphone and e-mail, said that his wife and their children had also been threatened with death. He told Europe 1 that his wife was in hiding with him, but he was less clear about his three children, saying that one of them had been forced to move and that another was in a boarding school.
Asked to describe the sort of threats he had received, Mr. Redeker replied, ''You will never feel secure on this earth. One billion, three hundred thousand Muslims are ready to kill you.''
Prime Minister Dominique de Villepin on Friday called the threats ''unacceptable,'' adding: ''We are in a democracy. Everyone has the right to express his views freely, while respecting others, of course.''
The Interior Ministry has confirmed that Mr. Redeker is under police surveillance, and that counterterrorism experts have begun a preliminary investigation into the threats, which the ministry has described as ''dangerous.'' Mr. Redeker complained in the radio interview that he had to arrange his own logistics and ''find a place to sleep at night or live for a day or two.''
One of the threats came from a contributor to Al Hesbah, who wrote, ''It is impossible that this day pass without the lions of France punishing him.''
The contributor called on his Muslim brethren in France to follow the lead of Muhammad Bouyeri, who murdered the Dutch filmmaker Theo van Gogh after he made a film denouncing the plight of abused Muslim women.
''May God send some lion to cut his head,'' the contributor said of Mr. Redeker, whom he described as a ''pig.''
Mr. Redeker's situation echoes that of Ayaan Hirsi Ali, a Somali-born Dutch politician who collaborated with Mr. van Gogh on the film and has been relentless in her criticism of some Islamic practices. The subject of numerous death threats from radical Islamists, she was put under the protection of bodyguards in the Netherlands in 2002, and currently has security protection in Washington, where she recently became a fellow at the conservative American Enterprise Institute.
In the Figaro commentary, Mr. Redeker wrote, ''Islam tries to dictate its rules to Europe: opening swimming pools at certain hours exclusively for women, forbidding the caricature of this religion, demanding a special diet for Muslim children in school cafeterias, fighting for wearing the veil in school, accusing free thinkers of Islamophobia.''
Mr. Redeker, who has written against Islam in the past, does not shy from controversy. At the time of the American-led invasion of Iraq, he criticized French pacifists, and he has written extensively about how watching sports competitions is worse than opium. His new book, ''Depression and Philosophy,'' is about to be published.
At first, Mr. Redeker did not speak out about the threats. In an e-mail message to The New York Times last Tuesday, he said it was not the right time to talk about his plight.
Then, in an interview with the local Toulouse newspaper, La Dépêche du Midi, published Thursday, Mr. Redeker described the death threats, adding, ''What is happening to me corresponds fully to what I denounce in my writing: the West is under ideological surveillance by Islam.''
That interview set off a public defense of Mr. Redeker in the name of free speech and condemnations of those who threaten him, which snowballed Friday after his radio interview with Jean-Pierre Elkabbach, the president of Europe 1, who is the host of a popular interview show.
Philippe de Villiers, a far-right politician, wrote President Jacques Chirac a letter on Friday asking that Mr. Redeker be given ''shelter -- as a symbol -- at the Élysée Palace, which is the palace of the republic, rather than let him wander,'' according to Agence France-Presse.
Le Figaro, in an unusual front-page open letter on Friday signed by the editor and the publisher, said, ''We condemn with the greatest conviction the grave attacks on freedom of thought and freedom of expression which this affair has provoked.''
On Thursday, Education Minister Gilles de Robien was less forceful. He expressed ''solidarity'' with Mr. Redeker, but cautioned that a ''state employee must show prudence and moderation in all circumstances.''
But two large teachers' unions in separate statements on Friday threw their support behind Mr. Redeker's right to speak freely, though one of them made clear, ''We do not share his convictions.''
Mr. Redeker said that he had no second thoughts about what he wrote. ''No regrets,'' he said in the radio interview. ''I have given a lot of thought in writing this text.''