The commission investigating the September 11, 2001 terrorist attacks says it wants to know why the Bush administration has withheld documents from the files of former President Bill Clinton.

A lawyer for Mr. Clinton, Bruce Lindsey, says Bush aides have turned over only a quarter of the 11,000 pages that Mr. Clinton was ready to offer the commission. The lawyer says that as a result, the commission may not have a complete picture of the Clinton administration's anti-terrorism efforts.

A spokesman for the commission, Al Felzenberg, says the panel is negotiating with the White House to determine what documents have been held back and why. He says the White House may have "good reasons" for its decision.

The New York Times cites former Clinton aides as saying the files contain highly classified documents about efforts to subdue al-Qaida, the group that carried out the September 11 attacks.

White House spokesmen acknowledge that some documents have been held back, saying the papers were not relevant to the investigation. The spokesmen say the Bush administration is giving the commission all the information it needs to do its job.

Presidential records are sealed by law for five years after a president leaves office. Under that provision, the Clinton administration's papers would be sealed until January, 2006. But an exception was made to allow early access for the September 11 commission.

Thursday, the commission said it will hear public and sworn testimony from National Security Adviser Condoleezza Rice on April 8.

The White House had originally refused to let Ms. Rice appear before the commission, but relented following public pressure.