A federal appeals court panel in Manhattan questioned a lawyer for the federal government yesterday as to whether the Central Intelligence Agency had a legitimate national security interest in refusing to confirm or deny the existence of documents authorizing it to detain and interrogate terrorism suspects overseas.

The tough questioning came in oral arguments by the American Civil Liberties Union and lawyers for the C.I.A. before the United States Court of Appeals for the Second Circuit. The civil liberties group is trying to force the C.I.A. to disclose how much authority it has been given to interrogate detainees since the attacks of Sept. 11, 2001.

Through the Freedom of Information Act, the A.C.L.U. is seeking documents, including a directive said to have been signed by President Bush, giving the agency the authority to set up detention sites outside the United States and to interrogate prisoners. In its lawsuit, the group says the existence of these documents has been hinted at in news reports.

But the government has refused to confirm or deny the documents' existence, saying that to do so would jeopardize national security by revealing C.I.A. methods and activities. Last September, Judge Alvin K. Hellerstein of Federal District Court upheld that position, and yesterday's hearing was part of the A.C.L.U.'s appeal of his ruling.