Members of both parties are accusing the White House of stonewalling the federal commission investigating the Sept. 11, 2001, attacks by blocking its demands for documents despite threats of a subpoena (search).

"I call on the White House to turn over the documents they are withholding from the independent commission -- and do it now," said Sen. Joseph Lieberman, D-Conn., co-author of the legislation that created the independent commission.

The 10-member, bipartisan commission has until May 27 to submit a report that also will deal with law enforcement, diplomacy, immigration, commercial aviation and the flow of assets to terror organizations.

"If they continue to refuse, I will urge the independent commission to take the administration to court," said Lieberman, who is running for president. "And if the administration tries to run out the clock, [Arizona Republican Sen.] John McCain and I will go to the floor of the Senate to extend the life of the commission."

Sen. Chuck Hagel, R-Neb., told a Sunday weekly interview program that it would be in the administration's interest to release documents the commission has requested.

"Americans and our allies across the globe must have confidence in our leadership," said Hagel, a senior member of the Senate Foreign Relations Committee (search) who has frequently criticized Bush's execution of the campaign against terrorists. "They must trust our processes. And that certainly includes our intelligence community's results."

White House spokeswoman Ashley Snee defended the administration's cooperation with the investigation and said the White House hoped to meet the commission's request for documents. At the president's direction, the executive branch has dedicated tremendous resources to the commission, including provision of more than 2 million pages of documents, Snee said.

Earlier this month, the independent commission voted to issue subpoenas to the Federal Aviation Administration (search) for documents pertaining to the investigation. The commission said the FAA subpoena will "put other agencies on notice that our document requests must be taken as seriously as a subpoena."

Commission chairman Thomas Kean (search), former Republican governor of New Jersey, told The New York Times in an interview published Sunday that he is prepared to subpoena documents from the White House if they are not turned over during the next several weeks.