In only the third time the Foreign Intelligence Surveillance Court (FISC) has publicly released a ruling, it turned back a request to reveal documents that would shed light on the government's program to spy on the communications of terror suspects without first obtaining warrants.

FISC's ruling argued that its role as a unique court dealing with national security issues necessarily meant its case documents and decisions would be classified, and that US constitutional provisions did not require it to release case materials.

It also said that even first deleting sensitive material from the papers sought by the American Civil Liberties Union -- secret documents related to the legality of the surveillance programs -- risked accidentally damaging the country's security.

"That possibility itself may be a price too high to pay," the court said in rejecting the ACLU request.

Jameel Jaffer, director of the ACLU National Security Project, called the decision disappointing.

"A federal court's interpretation of federal law should not be kept secret from the American public," Jaffer said.

"The Bush administration is seeking expanded surveillance powers from Congress because of the rulings issued by the Foreign Intelligence Surveillance Court earlier this year. Under this decision, those rulings may remain secret forever."

In August the ACLU sought access to FISC rulings and orders made earlier this year that were cited in a new law, the Protect America Act, which expanded the government's powers to spy on the international communications of US citizens without first seeking a warrant.

The civil liberties advocates argued that the public had a right to know the content of those rulings and orders as they were used by the government to widen the parameters of its surveillance powers.

In the decision signed by FISC judge John Bates, the court said that, even if the court first removed justifiably secret materials to oblige the ACLU request, it still "might err by releasing information that in fact should remain classified (and) damage to national security would result."