WASHINGTON - In an apparently serious setback for US 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 US 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 US officials said that the CIA informants, believed to be local recruits rather than US 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.

Hezbollah, founded with Iranian help during Lebanon's 1975-1990 civil war, has grown from a militia that fought Israeli forces in south Lebanon into the most powerful political and military force in the country. Hezbollah and its allies dominate the Lebanese government formed in June.

Baer said one reason Hezbollah has been successful in rooting out spies is that it is so powerful it has forced Lebanese government security forces to hand over sensitive communications and spy gear supplied by the US government. Hezbollah then used this US equipment to identify and track down CIA informants.

US officials were coy about the extent and seriousness of CIA losses. But they said damage to US intelligence was serious enough for extensive briefings and discussions to have been held with congressional oversight committees. A congressional source said any discussions remain classified.

Hezbollah, which the US government labels a terrorist group, and Iran, which it accuses of developing a nuclear weapon and sponsoring attacks on US troops in Iraq, are major targets of interest for US spy agencies and the White House.

There was no word about the unmasked operatives' fate.

The CIA declined to comment on the latest developments. Agency spokesman Preston Golson said the CIA "does not, as a rule discuss allegations of operational activities."

However, US officials explicitly denied a claim, reported by the Los Angeles Times on Monday, that CIA operations in Lebanon have effectively been crippled due to Hezbollah's

actions.

Nonetheless, US officials confirmed to Reuters that some CIA informants assigned to gather information on Hezbollah and the government of Iran had been compromised, and that any such losses are considered damaging to US intelligence collection efforts.

'EXTREMELY COMPLICATED ENEMY'

"Espionage has always been a perilous business. Collecting sensitive information on adversaries who are aggressively trying to uncover spies in their midst will always be fraught with risk," said one US official, speaking on condition of anonymity.

The official acknowledged: "Hezbollah is an extremely complicated enemy. ... It's a determined terrorist group, a power political player, a mighty military, and an accomplished intelligence organization formidable and ruthless. No one underestimates its capabilities."

During the past year, leaders of both Hezbollah and Iran have publicly touted what they said were successes by their security and counterintelligence forces in uncovering CIA informants.

In June, Hezbollah leader Sheikh Hassan Nasrallah said two of the group's members had been arrested on suspicion of being affiliated with the CIA, and a third was held for working either for the CIA or for European or Israeli intelligence agencies.

In May, Iran's intelligence minister said more than two dozen spies for the United States and Israel had been uncovered. ABC News reported that Iranian TV had broadcast what the US network described as accurate video of websites used by the CIA.

A former US intelligence official who worked in the region said US operatives have been "battling for most of the last decade" in a shadow war with what he described as Hezbollah's extremely effective counterintelligence operatives.

Over the years, Hezbollah has proven persistent, and sometimes successful, both in spotting CIA informants within its ranks and in trying to plant its own double agents on the CIA, the former official said.

One frequent tactic used by the group, the former official said, is to send "walk-in" operatives into US embassies in Middle Eastern and Mediterranean countries claiming to have information about attacks being planned against US targets.

Instead of having information about real attack planning, however, the "walk-ins" use their visits to US embassy buildings to gather information about embassy security measures and procedures which could then be used to plan possible attacks, according to the former official.

ASHINGTON - In an apparently serious setback for US 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 US 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 US officials said that the CIA informants, believed to be local recruits rather than US 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.

Baer said one reason Hezbollah has been successful in rooting out spies is that it is so powerful it has forced Lebanese government security forces to hand over sensitive communications and spy gear supplied by the US government. Hezbollah then used this US equipment to identify and track down CIA informants.

US officials were coy about the extent and seriousness of CIA losses. But they said damage to US intelligence was serious enough for extensive briefings and discussions to have been held with congressional oversight committees. A congressional source said any discussions remain classified.

There was no word about the unmasked operatives' fate.

The CIA declined to comment on the latest developments. Agency spokesman Preston Golson said the CIA "does not, as a rule discuss allegations of operational activities."

However, US officials explicitly denied a claim, reported by the Los Angeles Times on Monday, that CIA operations in Lebanon have effectively been crippled due to Hezbollah's actions.

Nonetheless, US officials confirmed to Reuters that some CIA informants assigned to gather information on Hezbollah and the government of Iran had been compromised, and that any such losses are considered damaging to US intelligence collection efforts.

'EXTREMELY COMPLICATED ENEMY'

"Espionage has always been a perilous business. Collecting sensitive information on adversaries who are aggressively trying to uncover spies in their midst will always be fraught with risk," said one US official, speaking on condition of anonymity.

The official acknowledged: "Hezbollah is an extremely complicated enemy. ... It's a determined terrorist group, a power political player, a mighty military, and an accomplished intelligence organization formidable and ruthless. No one underestimates its capabilities."

During the past year, leaders of both Hezbollah and Iran have publicly touted what they said were successes by their security and counterintelligence forces in uncovering CIA informants.

In June, Hezbollah leader Sheikh Hassan Nasrallah said two of the group's members had been arrested on suspicion of being affiliated with the CIA, and a third was held for working either for the CIA or for European or Israeli intelligence agencies.

In May, Iran's intelligence minister said more than two dozen spies for the United States and Israel had been uncovered. ABC News reported that Iranian TV had broadcast what the US network described as accurate video of websites used by the CIA.

A former US intelligence official who worked in the region said US operatives have been "battling for most of the last decade" in a shadow war with what he described as Hezbollah's extremely effective counterintelligence operatives.

Over the years, Hezbollah has proven persistent, and sometimes successful, both in spotting CIA informants within its ranks and in trying to plant its own double agents on the CIA, the former official said.

One frequent tactic used by the group, the former official said, is to send "walk-in" operatives into US embassies in Middle Eastern and Mediterranean countries claiming to have information about attacks being planned against US targets.

Instead of having information about real attack planning, however, the "walk-ins" use their visits to US embassy buildings to gather information about embassy security measures and procedures which could then be used to plan possible attacks, according to the former official.