It's hard – often impossible – to prove that secret government wiretapping in the name of national security is violating one's privacy rights. The evidence itself usually is top secret.

But one rather obscure case could pull back the veil on a surveillance program that's at the heart of the US fight against terror. In the federal appeals court in San Francisco Wednesday, lawyers for a Saudi charity accused of helping Al Qaeda will argue that their clients, including two American attorneys, were illegally spied on without the required court warrant.

How do they know? Treasury Department officials inadvertently provided them with National Security Agency (NSA) call logs stamped "top secret."

By the time federal agents had retrieved the logs of recorded calls six weeks later, the information had been shared with five other lawyers, two officials of the Al-Haramain Islamic Foundation's US branch in southern Oregon, and a reporter with The Washington Post.

Because the government took back copies of the call logs, federal judges at the district-court level agreed to let those who saw them rely on their memory of what they saw as evidence. The judges also said that they have "standing" in federal courts – that they have enough of a case to sue the federal government.

If the appeals court agrees with the lower court, the US Supreme Court is likely to become involved. The case could have broader significance as well since it deals with presidential power during wartime.

"The difficulty in challenging any secret program is in proving that you were a victim of it," says Jon Eisenberg, a lawyer in Oakland, Calif., who represents the now-defunct US arm of the Islamic charitable foundation. "We have that proof, and that makes us unique."

In recent days, the American Civil Liberties Union (ACLU) and the Center for Constitutional Rights (CCR) have issued new challenges to the federal government's domestic spying program.

In another case at federal district court in San Francisco last week, the CCR, which represents hundreds of "enemy combatants" at Guantánamo Bay, Cuba, argued that the NSA's program of warrantless surveillance is unconstitutional.

"It is virtually certain that the NSA spied on our confidential communications with our clients as well as conversations with other American attorneys outside of the US," says Vincent Warren, CCR executive director.

Meanwhile, the ACLU last week filed legal papers with the Foreign Intelligence Surveillance Court (FISC) – the special court set up to decide whether such wiretaps are lawful and can be implemented – seeking the legal opinions upon which that court bases its decisions.

ACLU attorneys argue that the only thing known about those opinions has come from administration officials, and that those officials are not disinterested parties in a debate about the appropriate reach of executive branch surveillance.

"The public has a right to firsthand information about what the court permitted and what it disallowed," says Jameel Jaffer, director of the ACLU's national security project. (Over the years, the secretive FISC has rarely denied wiretap requests.)

Just before they scattered for their August break, members of Congress made it easier for government agencies to eavesdrop on Americans in the name of fighting terrorism, raising once again the issue of domestic surveillance without a court warrant.

The administration characterized the just-passed change to the 1978 Foreign Intelligence Surveillance Act (FISA) as a way of keeping up with modern technology that didn't exist when the act was passed nearly 30 years ago: e-mail, the Internet, cellphones, and fiber-optic cables. Without the new law, President Bush said in signing it last week, US intelligence agencies would be "missing a significant amount of foreign intelligence that we should be collecting to protect our country."

The law is meant to allow the interception of suspicious foreign communications routed through the US. But it also allows intelligence agencies to intercept and record – without a court order – electronic communications involving Americans so long as the intelligence gathering is "directed at a person reasonably believed to be located outside the United States." And it gives the US attorney general and the director of national intelligence, rather than the special intelligence court, power to approve the international surveillance.

That's raised concerns among civil libertarians, who view it as a weakening of judicial oversight of wiretapping. They see it as echoing the Central Intelligence Agency abuses of the 1970s, which prompted Congress to pass FISA.

Since the new law has a six-month sunset provision, civil liberties advocates will be pushing Congress to enact greater safeguards – including judicial oversight – when lawmakers return to Washington next month.

In a letter to House Judiciary Committee chairman John Conyers (D) of Michigan, House Speaker Nancy Pelosi (D) wrote: "Many provisions of this legislation are unacceptable, and, although the bill has a six-month sunset clause, I do not believe the American people will want to wait that long before corrective action is taken."

Meanwhile, the Oregon wiretapping case to be heard before the Ninth US Circuit Court of Appeals this week may well reveal details directly related to the legality of domestic surveillance.

The government alleges that the Oregon-based chapter of the Saudi charity laundered $150,000 in donations to help Islamic fighters in Chechnya with ties to Al Qaeda. Attorneys for the group vigorously deny that charge. And they claim they were illegally spied upon, saying they've seen the government's own proof of that in the form of NSA phone logs.

Treasury and Justice Department officials refuse to comment on the case. But in court documents urging dismissal, administration officials wrote: "Whether plaintiffs were subjected to surveillance is a state secret, and information tending to confirm or deny that fact is privileged."