In federal courts and on Capitol Hill, challenges are brewing to a key legal strategy President Bush is using to protect a secret surveillance program that monitors phone calls and e-mails inside the United States.

Under grilling from lawmakers and attack by lawsuits alleging Bush authorized the illegal wiretapping of Americans, the White House has invoked a legal defense known as the "state secrets" doctrine — a claim that the president has inherent and unchecked power to shield national security information from disclosure, either to plaintiffs in court or to congressional overseers.

The principle was established a half-century ago when, ruling in a wrongful-death case brought by the widows of civilians killed in a military plane crash, the Supreme Court upheld the Air Force's refusal to provide an accident report to the plaintiffs. The government contended releasing the document would compromise information about a secret mission and intelligence equipment.

Sen. Arlen Specter of Pennsylvania, the senior Republican on the Judiciary Committee, believes the White House has gone too far in invoking state secrets to halt civil lawsuits.

"We have the authority to define the state secrets doctrine," Specter says. "I don't think that the simple assertion of state secrets ought to be the end of the matter."

Specter, Sen. Edward Kennedy, D-Mass., and others are working on legislation that would direct federal judges to review the president's state secrets claims and allow cases with merit to go forward.

Practices among judges vary. Some accept state secrets claims outright, dismissing cases on the government's word. Others read the privileged information and decide for themselves, but almost invariably side with the government, according to legal scholars.

The draft legislation is modeled on procedures used in criminal cases that involve classified information. The Classified Information Protection Act lets judges review classified information a criminal defendant wants to use in his defense, but which could compromise national security if it were released publicly. The law allows the court to delete classified passages, substitute summaries of the information, or substitute a statement of facts that the classified information would prove.

The measure could become part of the Senate's new eavesdropping law, expected to be voted on in early December, the aides said.

In another challenge to Bush's position on classified material, a federal judge in Virginia last week ordered the government to give trial prosecutors, defense lawyers and her clerk security clearances to review classified material in a terrorism case. Defense lawyers say the material will show the government failed to turn over evidence obtained by illegally monitoring their client's communications, and they want a new trial. The government says the information is protected by the state secrets privilege.

And in a case in Oregon, a U.S. district court judge is set to decide whether the 1978 Foreign Intelligence Surveillance Act trumps presidential claims of secrecy.

Adopted after the Watergate scandal, FISA dictates when the government must get permission from a secret court to monitor electronic communications inside the United States. It also allows people who believe they were spied on illegally to sue the government for damages and to request materials that would prove the surveillance. If the attorney general says disclosure would harm national security, a district court may review the classified materials privately to determine if the surveillance was illegal.

That civil liability provision of FISA, however, comes up hard against the National Security Agency's Terrorist Surveillance Program.

Shortly after the Sept. 11, 2001, attacks, Bush secretly authorized the spy agency to intercept international communications coming in and out of the United States that were believed to involve foreign terrorist organizations. It did so without going through the FISA court, claiming the Constitution and Congress' authorization for the use of military force after the terrorist attacks were all the authority the president needed to undertake the program.

Privacy and civil liberties groups say the warrantless surveillance violates FISA's prohibition on domestic surveillance without court orders. But for someone to sue the government for FISA violations, they must prove they were directly injured by the government's action. That is nearly impossible because the government will not disclose its targets or methods.

One organization, however, believes it can demonstrate it has standing to sue because of an accidental document release in 2004. That February, the Bush administration froze the assets of the Al-Haramain Islamic Foundation, a Muslim charity the United Nations Security Council alleges is associated with al-Qaida. In preparation for a legal proceeding on the terrorist designation in August, the Treasury Department inadvertently gave the foundation's lawyers and directors a top secret document dated May 24, 2004.

The document appeared to be a government summary of phone conversations it monitored between foundation lawyers and directors, according to a Washington Post reporter who received a copy from the foundation.

The FBI took the document from the Washington Post and Al Haramain in October 2004.

Fourteen months later, The New York Times revealed the existence of the Terrorist Surveillance Program. That is when the foundation's lawyers realized what the top secret document was: proof the organization had been targeted for warrantless electronic surveillance under TSP. They believe that proves standing, unique among plaintiffs in dozens of surveillance cases filed across the country.

The government asserts the states secrets privilege and refuses to release the document or confirm its contents. In its first crack at the case in 2006, the federal court in Oregon partially agreed. It said the document was rightfully protected by state secrets, but the foundation's lawyers could describe what they remembered about it to establish standing in their lawsuit.

The government appealed that decision to the 9th Circuit Court in San Francisco, which last week upheld its state secrets claim. But it did not dismiss the case. Instead, it directed the Oregon court to tackle one question it had sidestepped: whether FISA overrides the common law state secrets privilege.

Whatever the lower court decides, its decision will almost certainly be appealed to the Supreme Court, legal experts and attorneys on the case say. The high court is unlikely to be friendly to a challenge to the state secrets doctrine. In October it unanimously declined to hear a CIA torture allegation case that the Bush administration wanted dismissed on secrecy grounds. And in 2005, the Supreme Court unanimously upheld the state secrets doctrine in an espionage contract case.