President Bush and Vice President Dick Cheney have placed strict limits on the private interviews they will grant to the federal commission investigating the Sept. 11 attacks, saying that they will meet only with the panel's top two officials and that Mr. Bush will submit to only a single hour of questioning, commission members said Wednesday.

The commission, which has 10 members and is bipartisan, said in a statement that it had also been informed by the White House that Condoleezza Rice, the national security adviser, had rejected its request that she testify in public about the intelligence reports that reached her desk before the Sept. 11 attacks.

Democratic members of the panel said the administration's moves raised new questions about its willingness to cooperate with the commission, which is investigating intelligence and law enforcement blunders in the months and years before the 2001 attacks. The White House initially opposed creating the panel.

Republican Congressional leaders have criticized the investigation's pace. Speaker J. Dennis Hastert said he would not support and might block any legislation that extended the life of the panel, which is scheduled to complete its work in May.