Wednesday, January 11, 2006; A04

The National Security Agency's inspector general has opened an investigation into eavesdropping without warrants in the United States by the agency authorized by President Bush after the Sept. 11, 2001, attacks, according to a letter released late yesterday.

The Pentagon's acting inspector general, Thomas F. Gimble, wrote that his counterpart at the NSA "is already actively reviewing aspects of that program" and has "considerable expertise in the oversight of electronic surveillance," according to the letter sent to House Democrats who have requested official investigations of the NSA program.

Gimble's letter appears to confirm that an internal investigation into the NSA's domestic eavesdropping program, authorized by Bush in a secret order revealed in recent weeks, is underway. The Justice Department has opened a separate criminal investigation into the leak of the highly classified program's existence.

Officials in NSA Inspector General Joel Brenner's office could not be reached for comment last night.

A group of 39 House Democrats wrote Gimble and other officials last month requesting investigations into the legality of the NSA program. Gimble responded that his office would decline to launch its own investigation because of the ongoing NSA probe.

Another inspector general, Glenn A. Fine of the Justice Department, told the same group of lawmakers in a recent letter that his office does not have jurisdiction. The Democrats responded with a letter to Fine on Monday, arguing that both the inspector general statute and the USA Patriot Act require Fine's office to get involved.

Bush, who has joined his aides in an unusually public defense of the secret program, said last month that "the NSA's activities under this authorization are thoroughly reviewed by the Justice Department and NSA's top legal officials, including NSA's general counsel and inspector general."

Rep. Zoe Lofgren (D-Calif.) said NSA's inspector general should not be conducting an investigation if the office has played a role in approving the program.

"The inspector general for NSA has repeatedly reviewed this and okayed it, . . . so I don't know how his investigation is going to get a new set of eyes on this," Lofgren said. "How are they going to be able to investigate themselves?"

Justice officials said the request has been referred to the department's Office of Professional Responsibility. As the current attorney general and previous White House counsel, Alberto R. Gonzales played a central role in reviewing the wiretapping effort's legality and has strongly defended it in recent public statements.

Researcher Julie Tate contributed to this report.

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