The suit does not accuse Richard Armitage, who was deputy secretary of state in the Bush administration, of participating in an administration conspiracy to blow her cover.
Plame and her husband, former Ambassador Joseph Wilson, say the White House leaked Plame's identity as retribution for Wilson's criticisms of prewar intelligence on Iraq.
Armitage admitted last week that he told two reporters in 2003 that Plame worked for the CIA, but he said the disclosure was inadvertent. Armitage said he knew of no plan to leak Plame's identity; some people said that admission disproved the conspiracy theory.
By adding Armitage's name to the suit, Plame's lawyers set up a different scenario. They contend a White House conspiracy existed, but that Armitage's leak was independent of it.
Armitage is accused of violating Plame's privacy rights. He is not accused of violating the Wilsons' constitutional rights to equal protection and freedom of speech — allegations that remain against the White House officials.
Wilson discounted reports that then-Iraqi leader Saddam Hussein had tried to buy yellowcake uranium from Niger to make a nuclear weapon. Such a claim wound up in President Bush's 2003 State of the Union address.
Special Prosecutor Patrick Fitzgerald has investigated the leak for years and has not charged anyone with intentionally leaking Plame's identity. Libby is under indictment for lying to authorities about his conversations with reporters.