Washington ? After nearly three months behind bars, New York Times reporter Judith Miller was released from a federal prison Thursday after agreeing to testify in the investigation into the disclosure of a covert CIA officer’s identity, two people familiar with the case said.

Miller left the federal detention center in Alexandria, Va., after reaching an agreement with Special Counsel Patrick Fitzgerald. Legal sources said she would appear before a grand jury investigating the case this morning. The sources spoke on condition of anonymity because of the secrecy of the grand jury proceedings.

The sources said Miller agreed to testify after securing an unconditional release from Vice President Dick Cheney’s chief of staff, I. Lewis “Scooter” Libby, to testify about any discussions they had involving CIA officer Valerie Plame.

Miller has been held at the federal detention facility since July 6. A federal judge ordered her jailed when she refused to testify before the grand jury investigating the alleged leak of CIA officer Plame’s name by White House officials.

The disclosure of Plame’s identity by syndicated columnist Robert Novak in July 2003 triggered an inquiry that has caused political damage to the Bush White House and could still result in criminal charges against government officials.

The federal grand jury delving into the matter expires Oct. 28. Miller would have been freed at that time, but prosecutors could have pursued a criminal contempt of court charge against the reporter if she continued to defy Fitzgerald.

Of the reporters swept up in Fitzgerald’s investigation, Miller is the only one to go to jail. She was found in civil contempt of court on July 6.

Time reporter Matthew Cooper testified to the grand jury after his magazine surrendered his notes and e-mail detailing a conversation with presidential aide Karl Rove.

Novak apparently has cooperated with prosecutors, though neither he nor his attorney has said so.

Novak’s column on July 14, 2003, came eight days after Plame’s husband wrote in an opinion piece in the Times that the Bush administration twisted intelligence to exaggerate the threat from Iraq’s nuclear weapons program.

Novak wrote that two senior administration officials told him Plame had suggested sending her husband, former Ambassador Joseph Wilson, to the African nation of Niger on behalf of the CIA to look into possible Iraqi purchases of uranium yellowcake.

Wilson’s article in the Times had stated it was highly doubtful that any such transaction had ever taken place.

The timing of Wilson’s article was devastating for the Bush White House, which was struggling to come to grips with the fact that no weapons of mass destruction had been found in Iraq.