The White House says Mr. Bush has been "refreshing his memory" by meeting with key staffers and going over written material, reports CBS News Correspondent Peter Maer.
White House spokesman Scott McClellan insists the plan still calls for Mr. Bush and Cheney to appear together before the panel. McClellan rejects suggestions that they're appearing together to "get the story straight."
The meeting is expected to start at 9:30 a.m. on Thursday. White House Counsel Alberto Gonzalez and another legal staffer will likely be in the room.
The president and vice president will stay long enough to answer all the commission's questions, but neither leader will be under oath. Notes will be taken, but there will be no transcript by a stenographer, reports CBS News Correspondent Mark Knoller.
McClellan said Mr. Bush looks forward to the session and does not view it as adversarial.
The timing of the closed-door session was negotiated last week between the White House and the independent commission.
Initially, the president sought to limit his questioning to an hour and said he would only meet with the panel's chairman and vice chairman. But under heavy political pressure, Mr. Bush agreed to an open-ended session with all members. However, White House lawyers insisted the session include the vice president.
Public commission sessions have featured charges – hotly denied by the administration – that Mr. Bush and top aides downplayed the terror threat before Sept. 11 as they focused on Saddam Hussein's Iraq.
The issue of whether the 2001 attacks might have been prevented has dragged on in an election year, raising questions about the administration's actions in the months leading up to the attacks and potentially undercutting one of Mr. Bush's political strengths, national security.