Italian authorities reacted Wednesday to last week's bombings in London, tentatively blamed on four British citizens, by searching the homes of hundreds of suspected Islamic radicals and illegal immigrants.

Police and anti-terror units fanned out in Naples, Milan and other major cities, and searched homes and offices. Interior Minister Giuseppe Pisanu told reporters that the "maxi-blitz" showed that the government of Prime Minister Silvio Berlusconi has been alert to the possibility of attacks in Italy.

"The operation has been prepared for some time and confirms that Italy has never lowered its guard in the face of the terrorist tide," he said. "I'm not saying that we have seized terrorists. It's a preventive operation in high-risk environments." The police were looking for arms and explosives, officials said. No arrests were announced.

Authorities say they believe that Italy may be the next target of violence, following the bombings of transit systems in Spain and Britain, both allies of the United States in Iraq. Spain pulled its troops out of Iraq shortly after the March 11, 2004, attacks on four commuter trains in Madrid that killed 191 people and injured more than 1,800. Berlusconi has said that Italy will begin to withdraw its 3,000 troops from southern Iraq in September.

Italian intelligence officials closely monitor members of Islamic political organizations, as well as groups that allegedly have recruited radicals to fight in Iraq. Officials here say that for many years, Italy has served as a rear guard for operatives of Islamic terrorist groups. It is a place where enforcement of residency rules is lax and counterfeit documents are plentiful.

"If it is quiet here, it is not because we are so clever," a government official said. "It just means that no one wants to rock the boat in Italy." But many officials express concern that Italy's reprieve from attack will disappear.

Pisanu called on legislators to approve new anti-terrorism powers, which include doubling the time police can detain suspects in order to identify them from 12 to 24 hours, expediting the deportation of illegal immigrants, and mandating that Internet service providers retain e-mail traffic for an extended time.

Pisanu said people should be required to register when they purchase prepaid cell phones, and police should be given the right to question terrorism suspects without an attorney present.

Legal verdicts reached Wednesday provided a reminder of the potential danger that Italy faces. A judge in Brescia, in northern Italy, convicted two North Africans of membership in a cell that planned attacks in Italy, including one aimed at Milan's subway system.

The judge sentenced Mohamed Rafik, a Moroccan imam who preached at a mosque in Cremona, outside Milan, to four years and eight months in prison, and Kamel Hamraoui, a Tunisian, to 40 months. Najib Rouass, another Tunisian, was sentenced to 14 months on a charge of inciting violence. Another defendant was acquitted.

Police in Milan examine a trash bin as they increase patrols in the subway system.