WASHINGTON, Dec 17 (Reuters) - A member of the U.S. Senate Intelligence Committee on Tuesday disclosed the existence of a secret Central Intelligence Agency document that committee members believe supports their conclusions in a study highly critical of "waterboarding" and other harsh counterterrorism practices.
Senator Mark Udall, a Colorado Democrat, demanded the document - a CIA study of the interrogation techniques - at a confirmation hearing for Caroline Krass, President Barack Obama's nominee to be the CIA's general counsel.
Udall said he would not support Krass' nomination until the previously undisclosed document was provided, raising the possibility that he might use a "hold" to stop the nomination.
The intelligence panel's disagreement with the CIA over its 6,300-page report and the need for cooperation with Congress were a major focus of Tuesday's hearing, which also covered the nomination of Daniel Smith to be assistant secretary of state for intelligence and research.
The dispute over the report - and revelations by former contractor Edward Snowden about sweeping electronic surveillance by the National Security Agency - have sparked debate over whether congressional oversight of U.S. spy agencies is effective enough.
The Senate panel approved a draft of its report a year ago. But the CIA disputes many of its findings and has not met lawmakers' requests that parts of it be made public, leaving some senators frustrated at what they see as a lack of cooperation.
During the hearing, Krass told Senator Dianne Feinstein, who chairs the committee, that she did not believe members of the Senate panel had the right to see documents that provide the legal basis for CIA actions, such as waterboarding.
Maine Republican Senator Susan Collins said she was "troubled" by Krass' answer.
Udall asked Krass to ensure that the CIA provide the committee a copy of the internal review initiated under former CIA Director Leon Panetta of the agency's detention and interrogation program.
"It appears that this review ... is consistent with the Intelligence Committee's report, but, amazingly, it conflicts with the official CIA response to the committee's report," Udall said.
"If this is true, it raises fundamental questions about why a review the CIA conducted internally years ago and never provided to the committee is so different from the CIA's formal written response to the committee's study," he added.
The report's existence was not public knowledge until Udall questioned Krass during the hearing.
Committee Democrats have concluded that the CIA obtained little or no critical intelligence from its use of secret prisons and harsh interrogation. Several panel members offered tough criticism and closely questioned Krass over her view of such techniques.
"It (the use of such techniques) was a tragic mistake of great significance in the history of this country," West Virginia Senator Jay Rockefeller said.
Krass said she considered waterboarding to be torture.
Udall said he also wanted the White House to make a public statement committing to "the fullest possible declassification" of the committee's study, and the CIA's response, before he could support Krass' nomination.
Asked if Udall would use a hold, his spokesman Mike Saccone said the senator was committed to working with the committee and the CIA on the nomination and to get the information he requested.
But Saccone added: "He will have a full range of procedural tools to pick from to accomplish this objective." (Additional reporting by Mark Hosenball; Editing by Cynthia Osterman)