It's allowable. In fact I thought last decade some reporter went to prison for years for "contempt of court" for refusing to comply with a valid subpoena (but I forget the name).
Judith Miller was jailed for refusing to out Bush administration sources who outed Valerie Plame's status as a covert operative as political retribution.
Lewis Libby did not out Valerie Plame's status. It was reporter Robert Novak who did. It was also never 'leaked' as political retribution.
"In late August 2006, former U.S. Deputy Secretary of State Richard Armitage revealed publicly that Novak had based his disclosure of Mrs. Wilson's CIA identity on then still-classified information that Armitage initially gave him while Armitage was still serving in the State Department."
http://en.wikipedia.org/wiki/Plame_affair_timeline
The CIA assumed in the first half of the '90s that Aldrich Ames burned her covert status, so she was withdraw from that role long before any of this happened. Just another desk bound "operative" in McLean, Virginia, where there's a highway turnoff sign to the HQ.
I'm not sure what that has to do with anything. Outing a covert agent also risks outing other resources in the area, or sources and methods. In any case, it was clearly not a good idea for Scooter Libby to reveal her identity to Bob Novak.
