Senate Majority Leader Bill Frist and House Speaker Dennis Hastert are circulating a letter calling for a congressional leak investigation into the disclosure of secret U.S. interrogation centers abroad.

The Washington Post reported Nov. 2 on the existence of secret U.S. prisons in Eastern Europe for terrorism suspects. The Bush administration has neither confirmed nor denied that report.

"If accurate, such an egregious disclosure could have long-term and far-reaching damaging and dangerous consequences, and will imperil our efforts to protect the American people and our homeland from terrorist attacks," stated the letter, which Hastert's office said the House speaker had signed. There was no immediate word on whether Frist had given it his signature.

The Associated Press obtained a copy of the draft request to Senate Intelligence Committee Chairman Pat Roberts of Kansas and his House counterpart, Intelligence Committee Chairman Peter Hoekstra of Michigan.

Hoekstra's spokesman, Jamal Ware, declined to comment because the office had not yet received the letter.

The letter said a joint probe by the House and Senate intelligence committees should determine who leaked the information and under what authority.

"What is the actual and potential damage done to the national security of the United States and our partners in the global War on Terror?" the letter asked. "We will consider other changes to this mandate based on your recommendations."

House Minority Leader Nancy Pelosi said Republican leaders should also investigate possible manipulation of prewar intelligence on Iraq and the disclosure of covert CIA officer Valerie Plame Wilson's identity.

"If Speaker Hastert and Majority Leader Frist are finally ready to join Democrats' demands for an investigation of possible abuses of classified information, they must direct the House and Senate Intelligence Committees to investigate all aspects of that issue," said Pelosi.

The letter says the leaking of classified information by employees of the U.S. government appears to have increased in recent years, "establishing a dangerous trend that, if not addressed swiftly and firmly, likely will worsen."

"We are hopeful that you will be able to accomplish this task in a bipartisan manner given general agreement that intelligence matters should not be politicized," it added.

The Post story of a week ago said that the CIA has been hiding and interrogating some of its most important Al Qaeda captives at a Soviet-era compound in Eastern Europe, as part of a covert prison system set up by the agency four years ago that at various times has included sites in eight countries. The eight, said the story, include several democracies in eastern Europe.