Bruce Lindsey, former President Clinton's legal representative for records and a longtime confidant, told The Associated Press that the commission's attempt to get a full picture of Mr. Clinton's terrorism policies has been hampered because the Bush administration won't forward all of Mr. Clinton's records to the panel.
Lindsey said Mr. Clinton had approved the documents' transfer, but the White House has final authority on what is handed over. He said the White House has turned over only 25 percent of the 11,000 records requested by the commission.
The White House says it has fully met the panel's information requests.
According to the New York Times, White House spokesman Scott McClellan said some of the documents that have been withheld were "unrelated," while others were "highly sensitive."
"We are providing the commission with access to all the information they need to do their job," he said, according to The Times.
A spokesman for the commission told The Times the panel had sought an explanation from the White House, and was still waiting for one.
"If it did happen, it's an unintentional mistake or it's another intentional act of the White House that will backfire," commission member Bob Kerrey, a former Democratic senator, told the newspaper.
The Clinton administration's counterterrorism policy is at the heart of a dispute over whether the Bush administration ignored the threat of al Qaeda or inherited an inadequate policy from the Clinton team.
National security adviser Condoleezza Rice will testify in public before the commission next Thursday, CBS News Chief White House Correspondent John Roberts reports.
The questioning is likely to focus on what outgoing Clinton officials told Rice about the al Qaeda threat and her response afterward.
"She's obviously a very important witness who will be able to share the facts that pertain to the counterterrorism policy in the Bush administration, particularly in its earliest months," commission spokesman Al Felzenberg said. "The commission looks forward to hearing from her."
Rice had resisted testifying publicly in favor of meeting privately with the commission, citing legal concerns. But after mounting pressure, the White House this week agreed to let her appear before the panel after getting commission and congressional assurances that the move would not be seen as legal precedent that could force other presidential advisers before congressional panels.
Rice's testimony could have enormous implications for Mr. Bush's re-election campaign, which rests significantly on his national security credentials.
Mr. Bush's former counterterrorism chief, Richard Clarke, testified last week that the administration prior to Sept. 11.
Since Clarke's appearance, attention has turned to public statements the president and top aides made in the months before the terrorist attacks.
A CBS News review of speeches and public remarks by Mr. Bush suggests he did not mention al Qaeda once before Sept. 11, although he did send a letter to Congress extending sanctions against the Taliban for harboring al Qaeda and Osama bin Laden.
The Washington Post reported Thursday that on Sept. 11, 2001, Rice was due to make remarks that discussed national security threats, but never mentioned al Qaeda or bin Laden. Instead, the remarks focused on the need for missile defense.
The White House denied that the speech reflected a blind eye toward terrorism.
McClelland said, "this administration doesn't measure commitment based on one speech or one conference call or one meeting. We look at the sum total of the strong actions that we take."
On Thursday, the White House released portions of a top-secret document, finalized Sept. 4, 2001, that directed the Pentagon to draw up plans for attacking al Qaeda and Afghanistan's ruling Taliban. Any such action was seen as the last step in a three-to-five year plan, The Times reported.
Separately, Reps. Henry Waxman, D-Calif., and Carolyn Maloney, D-N.Y., each sent letters to White House counsel Alberto Gonzales asking him to explain why calls were placed to two Republicans on the Sept. 11 commission during Clarke's testimony.
The commissioners — Fred Fielding, a former White House counsel under President Reagan, and James Thompson, a former Illinois governor — questioned whether Clarke had political motives and pointed to earlier instances in which he praised the Bush administration's policies.
McClellan dismissed the notion that Gonzales provided the Republican commissioners with information about Clarke. "Judge Gonzales and the counsel's office is in contact with the commission all the time to make sure they have the information they need to do their job," he said.