Congress's top Republican leaders yesterday demanded an immediate joint House and Senate investigation into the disclosure of classified information to The Washington Post that detailed a web of secret prisons being used to house and interrogate terrorism suspects.

The Post's article, published on Nov. 2, has led to new questions about the treatment of detainees and the CIA's use of "black sites" in Eastern Europe and elsewhere. The issue dogged President Bush on his recent trip to Latin America and has created consternation in Eastern Europe.

"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," Senate Majority Leader Bill Frist (R-Tenn.) and House Speaker J. Dennis Hastert (R-Ill.) wrote in a letter to the chairmen of the House and Senate intelligence committees.

The letter requests that the committees "immediately initiate" a bicameral investigation. It also instructs the committees to refer to the Justice Department any information it uncovers that might constitute a violation of the law.

The CIA General Counsel's Office has also notified the Justice Department that a release of classified information took place in connection with the Post report, a senior administration official said yesterday. Such referrals are made at the rate of three to four per week, according to intelligence officials. But the notice is also the first step in a process that could lead to a criminal investigation, as happened in the Valerie Plame case.

The CIA will be required to fill out an 11-point questionnaire outlining the damage done by the release, how the information has been protected and the individuals or groups with knowledge of the information. Justice prosecutors will then determine whether they believe a criminal investigation is warranted.

A spokesman for The Post declined to comment on the letter from the congressional leaders. The article, by staff writer Dana Priest, said the CIA has operated a covert prison system that at times included sites in eight countries, including democracies in Eastern Europe. It cited as sources unnamed current and former intelligence officials and diplomats from three continents.

The Post did not publish the names of the Eastern European countries involved, at the request of senior U.S. officials. The article said the officials argued that the disclosure might disrupt counterterrorism efforts in those countries and elsewhere, and could make them targets of terrorist retaliation.

Congress has conducted fewer than a half-dozen bicameral investigations, reserving the process for the most pressing issues, such as the conduct of the U.S. Civil War and the illegal arms sales to Iran in the 1980s that were used to finance rebels in Nicaragua. The most recent House-Senate investigation came in 2002, when the intelligence committees looked into the Sept. 11, 2001, terrorist attacks.

Lawmakers from both parties immediately expressed misgivings about the request. Democrats pounced on it, suggesting that if the GOP leaders believe the disclosure of information on secret prisons deserves to be investigated, so does the leak of inaccurate intelligence on Saddam Hussein's weapons of mass destruction and White House officials identifying Plame as a covert CIA operative.

"There is plenty to investigate about the Bush administration's use and misuse of intelligence," said House Minority Leader Nancy Pelosi (D-Calif.). "The American people deserve the truth."

Rep. Christopher Shays (R-Conn.) said investigating the source of the prison article would be acceptable, as long as Congress also investigates the secret prisons themselves.

"If you want to investigate everything and not be selective, that would make sense," he said.

Sen. Lindsey O. Graham (R-S.C.) said: "Talk about not seeing the forest for the trees. The real story is those jails."

More generally, Republicans suggested it is unwise to pick a fight with the media over an issue that exposes so many political vulnerabilities for their party.

The emergence of the congressional leaders' letter came as a surprise to House intelligence committee Chairman Peter Hoekstra (R-Mich.) and Senate intelligence committee Chairman Pat Roberts (R-Kan.), both of whom said they learned of the request from the media. Roberts said that his committee "stands ready to be of service" but that he had "not received any marching orders from the leadership."

The marching orders laid out by Frist and Hastert are detailed and are requested in urgent language. Those orders include verifying that the information supplied to The Post was accurate and classified, identifying who leaked the information and under what authority, and detailing "the actual and potential damage done to the national security of the United States and our partners in the Global War on Terrorism."

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

White House spokesman Scott McClellan declined to say whether the president endorsed the probe, saying the decision belonged to the congressional leaders. But he did not offer any discouragement.

"The leaking of classified information is a serious matter and ought to be taken seriously," he told reporters.

Democratic leaders expressed their own concern about national security leaks, but in their case the emphasis was on the alleged release of Plame's name by indicted former White House aide I. Lewis "Scooter" Libby. Senate Minority Leader Harry M. Reid (Nev.), Pelosi and other Democrats sent two letters to Bush, urging him to declare publicly that he will not pardon Libby. Without such a declaration, Reid said, Libby will have no incentive to cooperate with Special Counsel Patrick J. Fitzgerald.

Staff writers Dan Eggen and Walter Pincus contributed to this report.

White House spokesman Scott McClellan said leaking classified information is "a serious matter" but did not indicate Bush's stance on an investigation.