WASHINGTON — FBI officials were so proud of a secret tunnel the agency built beneath the Soviet Embassy for electronic surveillance during the final years of the Cold War that they offered tours of the passageway to senior officials with top security clearances, former government officials said recently.
While much about the tunnel remains a closely held secret, electronic surveillance experts inside and outside the intelligence community said the tunnel operation gave the FBI the proximity it needed to intercept Soviet communications using a variety of bugs and taps.
"The closer the eavesdropper gets to the target, the more he can do," said one former government expert, explaining how tiny bugs planted throughout the embassy could have transmitted signals to the tunnel through fiber-optic and copper lines that are extremely difficult to detect.
"Any time you can get physical proximity to a target, it opens up a world of possibilities," said another expert who once worked for the National Security Agency, which provided the tunnel's eavesdropping technology.
Beyond "hard-wired" bugs directly connected to receivers in the tunnel, the experts said, the tunnel could have enabled the FBI to tap into telecommunications lines and even power cables, which carry electromagnetic signals that can be reconstructed and deciphered.
One former law enforcement official said laser technology was deployed in the tunnel, technology the experts said could have been used to capture sound waves emanating from pipes and structural support beams. One former government electronic surveillance guru said tiny microphones could even have been inserted in toilets through water pipes to monitor conversations in bathrooms.
But whatever technologies the NSA deployed to bug the embassy, the useful information it obtained was likely negligible, according to current and former government officials.
Prosecutors now believe that FBI agent Robert Hanssen tipped off the KGB to the tunnel's existence early in his alleged 15-year career as a spy for Moscow, nullifying the technological advantages the FBI could have gained from such close range.
One intelligence source with direct knowledge of the technology Hanssen allegedly compromised said the Soviets used the FBI bugs and wiretaps to feed disinformation back to the U.S. government.
"They were obviously feeding a very large quantity of data to us of apparent value but no real value," the source said. "It was a very delicate game that was played out over several years."
One former government official who was offered a tour but declined the invitation because he is claustrophobic said the tunnel was accessed from a residence near the Soviet — now Russian — compound on Mount Alto, a hilltop north of Georgetown between Wisconsin Avenue and Tunlaw Road NW that is one of the highest sites in Washington. The former official said the government purchased the home and started digging the tunnel out of its basement.
Another former official acknowledged that he had toured the passageway but declined to describe it, saying everything about it remains highly classified.
A 109-page affidavit filed in court to support espionage charges against Hanssen never specifically mentions the tunnel. But a senior U.S. official said the affidavit refers indirectly to the eavesdropping operation when it alleges that Hanssen "compromised an entire technical program of enormous value, expense and importance to the United States."
U.S. officials, in any event, realized the tunnel operation had been compromised years before Hanssen was unmasked last month as an alleged spy for Moscow, former FBI and intelligence officials said.
Indeed, Stanislav Lunev, a former colonel in Soviet military intelligence, said U.S. officials might have been alerted by a broadcast on Soviet television in 1987. In the broadcast, Soviet officials revealed numerous listening devices found throughout the embassy, including its basement.
"Somebody dug in the basement with a shovel and found electronic devices, brand new," said Lunev, who arrived in Washington under cover as a correspondent for the Soviet news agency Tass in 1988 and defected to the United States in 1992.
Lunev said he was never told that a tunnel existed but hardly finds the disclosure remarkable. "To believe there is no tunnel under the embassy would be stupid," Lunev said. "It's real life, a clear practice of intelligence."