The White House is in negotiation with the independent 9/11 commission in an attempt to defuse a damaging row over its refusal to allow Dr Condoleezza Rice to testify in public.
The bipartisan commission, which meets in closed session today, has asked unanimously that the national security adviser give evidence under oath.
White House spokesman Mr Scott McClellan said yesterday that the administration was discussing a second private appearance by Ms Rice, following four hours of unpublished testimony earlier this year. However he said there was no change in the White House position that, as a matter of principle, aides to the president do not testify publicly on policy issues.
Ms Rice declared on the CBS programme, 60 Minutes, on Sunday evening that "nothing would be better from my point of view than to be able to testify" but that it was "a long-standing principle that sitting national security advisers do not testify before the Congress".
A growing number of Democrats and Republicans have said that Ms Rice should make an exception to counter the public perception that she had something to hide. Former counter-terrorism aide Mr Richard Clarke testified to the 10-member commission under oath last week that President Bush and Ms Rice had not treated the terrorism threat as urgent in their eight months in office before the September 11th, 2001 attacks on the United States.
Republican Commission member Mr John Lehman called the refusal to testify "a political blunder of the first order".
Ms Rice also acknowledged on Sunday that Mr Bush had asked Mr Clarke at a meeting on the day after 9/11 to find out if Iraq had been involved in the terror attacks. Originally the White House said that President Bush had no memory of the meeting, first disclosed by Mr Clarke last week. "This was a country with which we'd been to war a couple of times, it was firing at our airplanes in the no-fly zone. It made perfectly good sense to ask about Iraq," Ms Rice said.
The national security adviser also told CBS that "the war on terrorism is well served by the victory in Iraq". When the interviewer said there had been more terrorist attacks in the 30 months since 9/11 than the same period before, she replied: "I think that's the wrong way to look at it." The terrorists will sometimes succeed but in the end, she said, "they are going to be defeated".