* Benghazi attack has become U.S. campaign issue
* Second site far better defended than consulate
* Security measures under tough Republican attack
By Mark Hosenball
WASHINGTON, Oct 10 (Reuters) - A public clash in Congress on Wednesday over photographs depicting the location of a second, semi-secret U.S. facility in Benghazi, Libya put the spotlight on a compound said to be more secure than the public American mission where U.S. Ambassador Christopher Stevens died last month.
When State Department officials, describing the chain of events on the night Stevens and three others died in a terrorist attack, displayed commercial satellite images of the two U.S. facilities, Rep. Jason Chaffetz, a Utah Republican, sharply accused them of divulging classified material.
"I was told specifically while I was in Libya I could not and should not ever talk about what you're showing here today," Chaffetz said at a hearing of the House Committee on Oversight and Government Reform. A congressional aide confirmed he was referring to the second site.
The existence of the second compound has been widely reported in accounts of the Sept. 11 violence in Benghazi, often being referred to as a "safe house" or "annex" to the temporary U.S. consulate. State Department officials at Wednesday's hearing said the photographs were not secret.
While the U.S. officials gave a fleeting public glimpse into the compound, they divulged little of substance on its purpose prior to the Benghazi attack, which has became an issue in the U.S. presidential campaign and the subject of multiple State Department and congressional probes.
Reuters, however, has learned some new details about it from U.S. officials, who spoke on condition of anonymity because of the issue's sensitivity and the ongoing official probes.
They described the second facility as a significant and largely secret complex, housing diplomatic and intelligence personnel. Among their assignments was a high-priority inter-agency program to locate shoulder-fired missiles and other weapons loosed by Libya's 2011 revolution. That program is coordinated by the State Department's Bureau of Political-Military Affairs.
The compound also housed a seven-man U.S. "quick-reaction security team" that went to the temporary consulate after Stevens and others came under attack there, according to testimony on Wednesday.
The two sites were about 1.2 miles (about two km) apart.
Several U.S. officials, speaking on condition of anonymity, said the second compound, which contained several buildings, including residential quarters for U.S. personnel, was far better defended than the temporary consulate where Stevens and IT specialist Sean Smith died.
After the consulate was overrun in an attack that began at 9:40 pm local time, U.S. and Libyan personnel retreated by car to the second site, where they fought off not one, but two, more waves of assaults, officials said.
Charlene Lamb, a top official in the State Department's Bureau of Diplomatic Security, told lawmakers that shortly after those retreating from the temporary consulate arrived at the second site, "the annex itself began taking intermittent fire for a period of time."
In the early morning of Sept. 12, after a backup U.S. security team arrived from Tripoli and went to the second site, "the annex started taking mortar fire, with as many as three direct hits on the compound," Lamb said.
Defenses at the second site largely held and unlike the temporary consulate, its grounds were not overrun. However, two U.S. security officials, Glen Doherty and Tyrone Woods, were killed there in what U.S. officials described as an unlucky mortar strike. The rest of the contingent eventually escaped to Benghazi's airport.
The assertions that the second site had relatively sophisticated defensive measures could raise additional questions about why the nearby consulate was not further reinforced given the volatile security environment in Benghazi.
Rex Ubben, whose son David was badly wounded in the attack on the second site and is being treated at Walter Reed National Military Medical Center, said his son had described an intense, sophisticated attack there.
The mortar fire's accuracy "indicates to me that someone was either very, very good, highly trained and skilled, or that the mortar was already set up and pointed at the 'safe house' and only minor adjustments were needed," Ubben, a 24-year Air Force veteran, told Reuters by email last week, relaying his son's account.
Secretary of State Hillary Clinton and other top U.S. officials have defended security measures in place at the temporary consulate, although those claims came under harsh attack by committee Republicans on Wednesday.
Officials investigating the attacks say there is evidence the State Department wanted to maintain a low security profile at the temporary consulate - which was the public face of the U.S. presence in the city - to project an appearance of normality in U.S. dealings with Libya.
Because Benghazi was regarded as lawless and violent, with a heavy presence of Islamic militants, the second compound's security measures included cameras and sensors and its security force included well-trained Americans like Doherty and Woods, the two former Navy SEALs who died in the mortar attack, the officials said.