ROME - As a second wave of London bomb attacks hit the news Thursday, Imam Khaldi Samir clicked nervously at his office computer, next to the prayer hall at the Alhuda Islamic Cultural Association on the outskirts of Rome. Bombs in London, he has seen, produce fallout for him.

Just two days earlier, with Italy stepping up surveillance after the first round of London attacks, 10 plainclothes police officers with a search warrant turned up at 7 a.m. at the imam's home in Latina, 70 kilometers, or 40 miles, south of Rome. During a three-hour raid, while his children slept, they scoured the home he shares with his Italian wife, and then downloaded numbers from his cellphone.

The police explained that they were looking for clues related to the London bombings, although they found nothing, said the imam, who preaches to up to 800 mostly poor immigrant worshipers each week. The search warrant did not indicate that the imam himself was suspected of a crime. Instead, the police politely explained, the search was "preventive" - the warrant stating he might have "unknowingly" had contact with people connected to terrorism. Five other leaders of the Italy's Muslims were searched the same day, he said.

"The state is punishing its best links to the Muslim community - we never expected that the Italian state would do something like this," said Samir, a soft-spoken man in a shirt and slacks, clearly shaken by the course of events.

"Every day I stress the need for moderation and integration," Samir said, "but these searches bring into question my credibility in our community. People will say, 'This is your payback for your moderation.'"

He said such events served to radicalize young people.

As antiterrorism officials across Europe are intensifying their hunt to root out sleeper cells, they walk a delicate line between thwarting terrorists and radicalizing innocent Muslims who are already largely isolated and marginalized in many European nations.

The challenge of controlling terrorism without creating new terrorists, is particularly acute in countries like France and Italy.

In those two countries, large and growing Muslim populations are kept by law and by custom on the fringes of mainstream society. There are an estimated 1.5 million Muslims in Italy, a country of about 58 million people. The vast majority of the Muslims are immigrants, who have little chance of getting citizenship. Less than 10 percent have an Italian passport.

An official at Italy's law enforcement agency, the Ministry of the Interior, said that he did not know specifics of recent raids, but that he was "not surprised" that such searches were occurring. "This is an ongoing process," he said.

On Friday, Italy's Council of Ministers adopted a series of new antiterrorism provisions, which are likely to take effect soon. These include new registration requirements for Internet cafés and cellphone users, new limits on pilots licenses, and quick expulsions for foreigners considered a danger to national security or who assist in terrorist activities.

But the search on the imam's house occurred legally under the current rules, which give judges wide leeway in issuing warrants.

"What if I had reason to believe that a terrorist had gone to your house and was worried he left something - some documents or even a suitcase?" said a senior Italian antiterrorism official, explaining the search.

In 2001, the police searched the Alhuda center, which includes a prayer hall and a cultural center and where Arabic and Islamic culture are taught to children. Last year, they searched the home of Ben Mohamed Mohamed, the center's president.

But since the attacks in London, the Italian government has beefed up security measures and has also attempted to reach out to Muslims. In Michelangelo's beautiful Campidoglio, on the afternoon of the second London bombings, the city of Rome invited prominent Muslims to convey a message of coexistence.

"Rome is a city that it open to everybody," said Giuseppe Mannino, chairman of the City Council. "You are our brothers."

He shared the podium with Mahmoud Hammad Sheweita, imam of Rome's only official mosque, the Grand Mosque - an architectural masterpiece filled with light and soaring arches, which operates with the permission and cooperation of the Ministry of the Interior.

Samir and Mohamed listened from the back row.

Unlike the Alhuda center, a subterranean former warehouse where young men wander in and out all day, the luxurious official mosque is open to worshipers only on Friday.

For the rest of the week, its primary function is to serve as a sort of liaison between Islam and the Italian government. From here, Mario Scialoja, a former Italian diplomat and convert to Islam, who is head of the Italian branch of the World Muslim League, meets with Islamic ambassadors and lobbies Italian politicians, pushing them to allow Muslims better access to citizenship, and religious education for Muslim children.

Scialoja said that the worshipers in his mosque, filled on Fridays, were typical Italian Muslims - poor immigrants who come to Italy for a better existence.

He said that "99.7 percent of them couldn't care less about fundamentalism" and that only 4 percent of Italy's Muslims attend mosque on a regular basis.

While he has noted some acts of intolerance since the London bombings, he praised Giuseppe Pisanu, the interior minister, whom he meets with regularly, and he called Italy's new antiterrorism proposals "very responsible." And though he blames the U.S. invasion of Iraq for creating terrorism, he does not support an immediate withdrawal. Italy has troops in Iraq in support of the U.S.-led invasion.

"To stay is to feed this anger, but to leave now would create a mess," he said.

But his official version of Islam seems to have little resonance or even connection with Samir's prayer hall, where many worshipers speak halting Italian and the lingua franca is Arabic.

When Scialoja tried to form a national association of Muslim groups five years ago, "the experiment was a failure," he said, "since some groups had views I couldn't support."

In 2003, when the Grand Mosque expelled its new Imam for a fiery sermon that justified Palestinian bombings in Israel (though not in Italy), Alhuda's Web site posted an article defending his right to free speech.

In part because Italy does not recognize Islam as a religion, Samir's flock does not have a real mosque. Italian Muslims must work on their religion's holy days. As aliens, the vast majority have no right to vote.

"Now, with the increasing security, they search our houses - this is a very bad sign," Samir said. "We hear all about the policies on integration, but we never seen any concrete measures."

They remain largely outsiders and, especially now, visitors to the Alhuda center and the surrounding Islamic shops were greeted with intense suspicion. Requests to interview the Imam were met with deflections and questions: Where are you from? Why do you want him?

Samir, a Tunisian who has lived in Italy for 15 years, insists that he would report suspicious activity to the police.

Asked if anyone from the Alhuda had attended the religious schools in Pakistan that have been a breeding ground for terrorists, he said: "Not that I know of, but they certainly wouldn't tell me if they had."