MILAN  In a landmark ruling, an Italian judge on Wednesday convicted a base chief for the Central Intelligence Agency and 22 other Americans, almost all C.I.A. operatives, of kidnapping a Muslim cleric from the streets of Milan in 2003.

The case was a huge symbolic victory for Italian prosecutors, who drew the first convictions involving the American practice of rendition, in which terrorism suspects are captured in one country and taken for questioning in another, often one more open to coercive interrogation techniques.

Critics of the Bush administration have long hailed the case as a repudiation of the tactics it used to fight terrorism. And the fact that Italy would actually convict intelligence agents of an allied country was seen as a bold move that could set a precedent in other cases.

Still, the convictions may have little practical effect. They do not seem to change the close relations between the United States and Italy. Nor did they reveal whether the government of Prime Minister Silvio Berlusconi had approved the kidnapping. And it seemed highly unlikely that anyone, Italian or American, would spend any time in prison.