A total of 423 people were initially questioned during the sweep in Rome, Turin, Florence, Bologna, Naples and other cities, but most were later released.
“The operation has been prepared for some time and confirms Italy has never lowered its guard in the face of terrorist risks,” Interior Minister Giuseppe Pisanu said.
The crackdown, involving 201 search warrants, follows last week’s London attacks and comes a day after Mr Pisanu warned that terrorism was “knocking on Italy’s door” and urged parliament to strengthen security laws.
“I’m not saying that we have seized terrorists. It’s a preventative operation in high-risk environments,” he said.
The ministry said those detained were not under formal arrest, but were among hundreds of people being checked out, some over their legal status in Italy.
The search warrants were issued to look for illegal arms and explosives, a spokesman said.
Police said they were investigating a wide range of crimes, from falsifying documents to terrorism.
On Tuesday Mr Pisanu called for stronger controls at Italy’s borders and an extension of the period a suspect can be detained for identification from 12 to 24 hours, among other measures.
France has taken measures since the London attacks, by activating a clause in the Schengen open borders agreement enabling it to reintroduce border controls within the EU.
Meanwhile EU ministers have committed to implementing security laws agreed on a year ago after the Madrid attacks.
French Interior Minister Nicolas Sarkozy said equipment had to be developed to enable finger printing of all people seeking visas within the Schengen open border zone, and backed Britain on a law giving police access to telecommunications data.
The measure could see data from telephones — mobiles, text messages and landlines — and Internet information like e-mail kept for at least a year.
Other measures included improving police cooperation and information sharing, finding out what makes people turn to terror, and revising shipping and aviation security.
British Home Secretary Charles Clarke has also called for EU states to agree common standards for security features on identity cards as well as rules to combat terror financing.
British Prime Minister Tony Blair said his government would consider tougher action against people who incite terrorism, including tighter entry procedures, as well as promoting moderate Islam at home and abroad.