ROME - An Italian judge convicted 23 Americans yesterday of kidnapping an Egyptian cleric off the streets of Milan in 2003, a sweeping verdict against one of the CIA's most valued antiterrorism tools - the practice known as extraordinary rendition.

The decision was a victory for Italian antiterrorism prosecutors and police who spent six years building a massive case. The two-year trial exposed details of a secretive world and was the first anywhere to challenge the program under which the CIA abducted suspects and spirited them to third countries for interrogation.

A clandestine team of U.S. and Italian operatives abducted Abu Omar, an extremist cleric suspected of recruiting fighters for Iraq and Afghanistan, and he was flown to Egypt, where he claimed to have undergone months of torture and abuse.

The case sparked international uproar, and the governments of Italian Prime Minister Silvio Berlusconi and his predecessor tried repeatedly to scuttle the trial.

Judge Oscar Magi acquitted three other Americans, including the former CIA station chief in Italy, because they had diplomatic immunity. Magi also set aside charges against five Italian intelligence officials including the former chief and deputy chief of Italy's spy agency, ruling they were protected by a state-secrets law. But he convicted two other Italians.

The Americans were tried in absentia. Given that the U.S. government has declined to cooperate with the prosecution, it seemed unlikely that any would spend time in an Italian prison. However, the convicted Americans may be at risk if they travel to Europe. Prosecutors have issued arrest warrants that can be executed in any of the European Union's 27 countries.

The judge issued an eight-year prison sentence for Robert Seldon Lady, the former CIA chief in Milan. Testimony indicated that Lady initially opposed abducting Abu Omar as unnecessary and dangerous but ultimately became the ground-level architect of the operation. The other U.S. operatives were given five-year sentences, and the Italians received three-year terms.

With the help of Lady, Italian police had already been investigating Omar. But Lady was alleged to have orchestrated the kidnapping without their knowledge. The operation on the streets of a close ally caused bad blood among U.S. and Italian antiterrorism officials and within antiterrorism agencies in both countries, according to testimony.

Italian intelligence officials testified that the station chief in Rome, Jeff Castelli, and other officials pushed for the rendition, possibly hoping to recruit Abu Omar as an informant. The CIA deployed a paramilitary squad, aided by Italian operatives, that stalked Abu Omar for weeks before snatching him.

In a wiretapped phone call to his wife and later in public statements, the Egyptian alleged that his country's security forces had tortured him and locked him in a rat-infested cell. Egyptian authorities eventually released him, but they did not allow him to return to Italy to testify.

Probably because they had clearance from Italian spymasters, the U.S. operatives left a trail of cell-phone calls, credit-card charges, and photo-identification documents. The evidence enabled an elite antiterrorism unit of the Italian police to assemble a detailed case that became an anatomy of a rendition.

"The Milan court sent a powerful message: The CIA can't just abduct people off the streets," said Joanne Mariner, terrorism program director at Human Rights Watch. "It's illegal, unacceptable, and unjustified."