You're right, he literally can't under the law.
If she was legally "covert", and Fitzgerald revealed that, he'd be breaking the law.
Saying that her position was/is "classified", though, is not a breach of the law.
Please. The whole bleating of the Left revolves around the point that poor Plame's status has now been IRREPARABLY BLOWN.
If she's "legally covert" even now---such that, as you argue, it would be illegal for Fitzie to reveal her status---then both she and her hubby have violated the law many times.
No self-respecting covert agent would do a photo shoot for Vanity Fair while in a covert status.
No covert agent worth her salt would conclude that her husband can write op-eds for the NYT attacking the current administration without foreign operatives nosing around and discovering that the author's wife was CIA.
Etc.
What you are arguing is that, irrespective of the practical fact that Plame's cover (such as it was) has been blown, Fitzie can't reveal her (for the purpose of argument) covert status without violating the law.
Would not the acts and statements of Mr. and Mrs. Wilson have violated the same law?
Or are we going to make a "very fine distinction" here and claim that all Mr. and Mrs. Wilson did was acknowledge that Plame worked at the CIA, not acknowledge her "covert" status.