The Pentagon and to a lesser extent the CIA have been using a little-known power to look at the banking and credit records of hundreds of Americans and others suspected of terrorism or espionage within the United States, officials said Saturday.

Pentagon spokesman Bryan Whitman said Saturday the Defense Department "makes requests for information under authorities of the National Security Letter statutes ... but does not use the specific term National Security Letter in its investigatory practice."

Whitman did not indicate the number of requests that have been made in recent years, but said authorities operate under the Right to Financial Privacy Act, the Fair Credit Reporting Act and the National Security Act.

"These statutory tools may provide key leads for counterintelligence and counterterrorism investigations," Whitman said. "Because these are requests for information rather than court orders, a DOD request under the NSL statutes cannot be compelled absent court involvement."

"It is our understanding that the intelligence community agencies make such requests on a limited basis," said Carl Kropf, a spokesman for the Office of the National Intelligence Director, which oversees all 16 spy agencies in the government.

The national security letters permit the executive branch to seek records about people in terror and spy investigations without a judge's approval or grand jury subpoena.

The Federal Bureau of Investigation, the lead agency on domestic counterterrorism and espionage, has issued thousands of national security letters since the attacks of Sept. 11, 2001.

Whitman said Defense Department "counterintelligence investigators routinely coordinate ... with the FBI."

The national security letters have prompted criticism and court challenges from civil liberties advocates who claim they invade the privacy of Americans' lives, even though banks and other financial institutions typically turn over the financial records voluntarily.

The New York Times reported on expanded use of the technique by the Pentagon and CIA in an article posted Saturday on the Internet.

The vast majority of national security letters are issued by the FBI, but in very rare circumstances they have been used by the CIA before and after 9/11, said a U.S. intelligence official who spoke to The Associated Press on condition of anonymity because of the issue's sensitivity.

The CIA has used these non-compulsory letters in espionage investigations and other circumstances, the official said.

"It is very uncommon for the agency to be issuing these letters," the official said. "The agency has the authority to do so, and it is absolutely lawful."

Another government official, also speaking on condition of anonymity, said one example of a case in which the letters were used was the 1994 case of CIA officer Aldrich Ames, who eventually was found to have been selling secrets to the Soviet Union.

None of the officials reached by the AP commented about the extent of use by the Defense Department agencies, but the Times said military intelligence officers have sent the letters in up to 500 investigations.