At the direction of the then-vice president, Congress was not notified of a highly classified counter-terrorism program for eight years, sources say.

    Washington - The CIA kept a highly classified counter-terrorism program secret from Congress for eight years at the direction of then-Vice President Dick Cheney, according to sources familiar with an account that agency Director Leon E. Panetta provided recently to House and Senate committees.

    The sources declined to provide any details on the nature of the program, but said that the agency had opened an internal inquiry in recent days into the history of the program and the decisions made by a series of senior officials to withhold information about it from Congress.

    Cheney's involvement suggests that the program was considered important enough by the Bush administration that it should be monitored at the highest levels of government, and that the White House was reluctant to risk disclosure of its details to lawmakers.

    Panetta killed the program on June 23 after learning of it, four months after he became director of the CIA. He then called special sessions with the House and Senate intelligence committees.

    The CIA's relationship with Congress has become a source of controversy in Washington in recent months, after House Speaker Nancy Pelosi (D-San Francisco) accused the agency of lying to members about its use of waterboarding and other interrogation measures in the aftermath of the Sept. 11 attacks.

    The secret counter-terrorism program was put in place shortly after those attacks, but it was never fully operational, sources said. Current and former intelligence and congressional officials have offered different viewpoints on the program's significance.

    A senior congressional aide said the magnitude of the program and the decision to keep it secret should not be downplayed. "Panetta found out about this for the first time, and within 24 hours was in the office telling us," the aide said. "If this wasn't a big deal, why would the director of the CIA come sprinting up to the Hill like that?"

    An aide to Cheney did not respond to a request for comment. CIA spokesman Paul Gimigliano declined to comment Saturday on the program or Cheney's role, which was initially reported by the New York Times on its website.

    By law, the CIA is required to make sure that congressional committees are "kept fully and currently informed of the intelligence activities of the United States, including any significant anticipated intelligence activity."

    But there is latitude in the language for programs and operations deemed extremely sensitive, or those that might be considered routine.

    Indeed, former U.S. intelligence officials said that Panetta's predecessors, including retired Lt. Gen. Michael V. Hayden, did not think they were constrained from informing Congress about the program, but regarded the activity as falling well short of the threshold for congressional notification.

    "We do a lot of foreign intelligence collection we don't run down to the Hill and say, 'How about this?' " said a former U.S. intelligence official familiar with the program, who spoke on condition of anonymity.

    More than a year ago, however, Hayden informed subordinates that the intelligence committees would need to be briefed on the program if it crossed certain thresholds, according to former officials.

    The key issue, the officials said, was whether the agency was taking steps in its implementation of the program that could potentially be discovered by foreign intelligence services, and therefore possibly surface publicly -- to the embarrassment of the United States.

    The program was coming "closer to [being] something in the real world" when Hayden issued the guidance, one former official said. But the activity never reached that point.

    Hayden was among the high-level CIA officials -- including Deputy Director Stephen Kappes and the head of the clandestine service, Michael J. Sulick -- who were kept apprised of the program's progress.

    One former official said that Hayden, Kappes and Sulick were "very cautious" in their handling of the program and that they made decisions to narrow its focus.

    The official said that the program fell on a continuum between foreign intelligence collection and covert action; the latter involves taking steps to influence events overseas, and generally falls within more stringent congressional notification rules.

    Some former high-level CIA officials said they remained puzzled about which program could be at the center of the budding controversy.

    "A lot of people thought they were Jason Bourne and came up with ideas," said a former senior CIA officer, referring to the fictional super-spy. "There were programs that were kind of wild that were considered in 2001, but to my knowledge, within six months we didn't get one follow-on attack and people kind of gave up on those ideas."

    The House Intelligence Committee has approved new legislation that would seek to make it significantly more difficult for the executive branch to withhold information on intelligence activities from Congress. But President Obama has threatened to veto the legislation.