The legal filing with the 2nd Circuit U.S. Court of Appeals in New York comes amid a debate in Congress over renewal of the Patriot Act and whether to expand the FBI's power to seek records without the approval of a judge or grand jury.

U.S. District Judge Victor Marrero of New York last year blocked the government from conducting secret searches of communications records, saying the law that authorized them wrongly barred legal challenges and imposed a gag order on affected businesses.

The ruling came in a lawsuit by the American Civil Liberties Union and an Internet access firm that received a national security letter from the FBI demanding records. The identity of the firm remains secret.

The government was authorized to pursue communications records as part of a 1986 law. Its powers were enhanced by the Patriot Act in 2001.

The administration said the judge's ruling was off the mark because the company did mount a legal challenge to the demand for records. "Yet in this very case, the recipient of the NSL did precisely what the NSLs supposedly prevent recipients from doing," the filing said.

The law's ban on disclosing that such a letter has been received also is appropriate because of legitimate security concerns, the government said.

But ACLU attorney Jameel Jaffer said the law does not contain a provision to challenge the FBI's demand for documents. The ACLU and the firm filed the lawsuit to challenge the law's constitutionality on the grounds that it doesn't contain such a provision, he said.

"Most people who get NSLs don't know they can bring a challenge in court because the statute doesn't say they can," he said. "No one has filed a motion to quash in 20 years."

The ban on disclosure is so broad that the ACLU initially filed the suit under seal and negotiated for weeks on a version that could be released to the public.

Previously censored material released several months after Marrero's ruling included innocuous material the government wanted withheld, the ACLU said, including the phrase "national security" and this sentence from a statement by an FBI agent: "I am a Special Agent of the Federal Bureau of Investigation."