The CIA took the first step toward a full-scale criminal investigation of a leak of possibly classified information on secret prisons to The Washington Post, a U.S. official said Tuesday.

The agency's general counsel sent a report to the Justice Department about the Post story, which reported the existence of secret U.S. detention centers for suspected terrorists in Eastern Europe.

The official, who spoke on condition of anonymity because the issue deals with classified information, said the referral was made shortly after the Nov. 2 story. The leak investigation into the disclosure of covert CIA officer Valerie Plame's identity came about through the same referral procedure. The Justice Department will decide whether to initiate a criminal investigation.

The Post declined to comment.

On Capitol Hill, Senate Majority Leader Bill Frist and House Speaker Dennis Hastert called for a congressional investigation into the disclosure of the existence of the secret prisons.

Secretary of State Condoleezza Rice sidestepped questions on secret prisons, saying the United States was in a "different kind of war" and had an obligation to defend itself.

If the Post story is 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," wrote Frist, R-Tenn., and Hastert, R-Ill., asking for a joint leak probe by the Senate and House intelligence committees.

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

"If the leadership determines that we should investigate the leak, it would be much like the 9/11" commission, said Senate Intelligence Committee chairman Pat Roberts, R-Kan., who did not dispute a reporter's suggestion that a probe would raise First Amendment press-freedom issues.

Such an investigation would become "very difficult when you're getting into matters like this," said the senator.

Roberts also said he would support hearings into the importance of maintaining a covert agent's cover, a topic triggered by the leak of Plame's identity, eight days after her husband accused the Bush administration of manipulating prewar intelligence to exaggerate the Iraq threat.

Democratic leader Harry Reid of Nevada said the House and Senate committees with normal jurisdiction should conduct any hearings, not a bicameral committee as suggested in the letter of the two Republican leaders.

House Minority Leader Nancy Pelosi, D-Calif., said any such joint investigation should also investigate possible manipulation of prewar intelligence on Iraq.

"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 asked, concerning the leak of information about prisons, "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?"

"We will consider other changes to this mandate based on your recommendations," Frist and Hastert wrote.

The letter said the leaking of classified information by employees of the U.S. government appeared 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.

While not confirming the existence of secret prisons, Rice told reporters, "We, our allies, others who have experienced attacks, have to find a way to protect our people."

The administration has protected itself "within the constraint of the Constitution and cognizant of our values," said Rice. "The United States holds to these values today as strongly as we ever have."