Valerie Wilson, the former intelligence operative at the heart of an investigation that reached into the White House, sued the Central Intelligence Agency in federal court in New York yesterday over its refusal to allow her to publish a memoir that would discuss how long she had worked for the agency.

Although that information is set out in an unclassified letter to Ms. Wilson that has been published in the Congressional Record, the C.I.A. contends that her dates of service remain classified and may not be mentioned in “Fair Game,” the memoir Ms. Wilson hopes to publish in October.

C.I.A. employees sign agreements requiring them to submit manuscripts to the agency for permission before they are published, and Ms. Wilson’s suit said she spent 10 months working with agency officials on the book to avoid disclosing national security information. But the agency’s refusal to allow her to include material already in the public domain, the suit said, violates her right to free speech.

“The C.I.A.’s effort to classify public domain information is an unreasonable attempt at prior restraint of publication and a violation of our First Amendment rights,” said Adam Rothberg, a spokesman for Simon & Schuster, which plans to publish the book and is also a plaintiff in the suit.