TEHERAN (AP) - Sayeed Habibi considers himself a marked man. The reason: his Internet blog that challenges some of the policies of Iran's theocracy. He predicts that someday - perhaps soon - he'll be taken to prison and his site will be shut down. "And another voice will be silenced," said Habibi, a 34-year-old postgraduate and an unofficial elder statesman for student-led activist movements. "I fully expect to see the inside of a jail cell." He's not alone. Iranian authorities are stepping up arrests and pressure on popular bloggers as part of a wider Internet clampdown launched after hard-liner Mahmoud Ahmadinejad became president last year, ending years of freewheeling Web access that once made Iran among the most vibrant online locales in the Middle East. The Internet censors are busy. Their targets include sexual content, international politics, local grumbling, chat rooms and anything else that makes the Islamic leadership uneasy. Mohammad Ali Dadkhah, a prominent human rights lawyer, estimates at least 50 bloggers have been detained since last year. Thousands of Web sites have been blocked, including anti-regime groups from Iranians abroad and news outlets such as the British Broadcasting Corp.'s Persian Service and the Voice of America. But it remains a spotty assault. Sites such as The Jerusalem Post and California-based regimechangeiran.com remain accessible. The cyber-squeeze, however, is seen as more than a broad slap at dissent. It shows vividly what authorities can and can't control. The Islamic establishment is able to filter the Web through its oversight of all Iran's Internet service providers, as well as media, cinema, literature and other arts. But conservatives have - at least in recent years - essentially given up on street culture. Women continually push the limits with ever tighter and more revealing scarves and jackets. Any type of Western music or Hollywood blockbuster is easily available with the right connections. Satellite dishes are officially restricted, but sprout up everywhere. The Internet is still up for grabs. Web surfers can use peer-to-peer sites - sometimes called "data havens" - that bypass the state-controlled servers. So far, the authorities are struggling to keep pace. "It's the classic Iranian battle of freedom against controls," said Isa Saharkhiz, a member of the Iranian branch of the Committee to Protect Journalists. "The crackdown on bloggers is part of a growing censorship policy by the state." Iranian bloggers first started proliferating about five years ago. There even was a sense of official encouragement after then Vice President Mohammad Ali Abtahi went online. Soon, hundreds were blogging in both English, Farsi and a hybrid of Farsi spelled in Latin characters. Most used pseudonyms, but no subject was taboo: sex, off-color jokes, personal confessions, and dumping on the ruling clerics. One blogger's chat room included a rant about the likes and dislikes of the theocrats. Listed among "the mullahs' favorite statesmen" were Adolf Hitler, Josef Stalin, Pol Pot, Fidel Castro and Robert Mugabe. An Iranian bilingual blogger known as "scarecrew" grumbled in English: "Sometimes I feel like I'm living in an island. What is it that they don't want us to know?... No matter how, I just wanna get myself out of this place." Another, "Iran Shadow," lashed Ahmadinejad for "pursuing polices that are reminiscent of some of the darkest days of the Islamic Republic." Officials began fighting back last year. Ahmadinejad's election, coupled with the conservative sweep of parliament in 2004, left liberals powerless. Bloggers face more than being unplugged. Those detained are charged under anti-subversion laws that carry a maximum sentence of five years. Convictions so far have been largely suspended sentences. "Every day, we see violations of international rules and norms by this government," said Dadkhah, who has represented many of the bloggers along with fellow lawyers who formed the Center for Protecting Human Rights. On August 5, authorities banned the group, which included Nobel Peace Prize laureate Shirin Ebadi. One of Dadkhah's highest-profile clients, Teheran University student Abed Tavancheh, was arrested in late May and accused of fomenting student unrest with his political blog. Dadkhah claims Tavancheh, 23, was severely beaten in prison and suffered kidney damage before his release on bail in July. No trial date has been set. The case has been publicized by free speech groups such as Reporters Without Borders. Tavancheh refused a request for an interview, but his friend, blogger Habibi, said he has returned to his family's home in Arak in central Iran and is undergoing medical treatment. "He is frightened," said Habibi. "He is away from his friends and his studies. The regime is trying to teach us a lesson: Be quiet and meek or we'll come after you. We refused to be silent and looked what happened." Habibi, Tavancheh and four others posted letters on their blogs in April calling for a national dialogue on Iran's nuclear energy program, which the West fears could be cover for atomic weapons development.