In an apparently serious setback for U.S. intelligence against a key adversary, Hezbollah, the Lebanese Shi'ite militia, has succeeded in identifying and arresting informants within its ranks who were working for the CIA, current and former U.S. officials said.

Separately, counterintelligence officers in Iran also succeeded in uncovering the identities of at least a handful of alleged CIA informants, the officials said.

Some former U.S. officials said that the CIA informants, believed to be local recruits rather than U.S. citizens, were uncovered, at least in part, due to sloppy procedures - known in the espionage world as "tradecraft" - used by the agency.

But Bob Baer, a former CIA operations officer whose books inspired the Hollywood movie Syriana, said that Hezbollah's counterintelligence capabilities are formidable and should not be underestimated.

"Hezbollah's security is as good as any in the world's. It's the best. It's better than that of the KGB," the former Soviet spy agency, Baer said.