Washington ? A federal prosecutor investigating whether administration officials illegally leaked the name of an undercover CIA operative has directed considerable effort at learning how widely the operative’s identity was disseminated to reporters before it was published last year by columnist Robert Novak, according to people with knowledge of the case.

Special prosecutor Patrick Fitzgerald is trying to pinpoint precisely when and from whom several journalists learned that Joseph C. Wilson IV, an outspoken critic of the administration, was sent on an Iraq-related intelligence mission after a recommendation by his wife, Valerie Plame, a covert CIA employee. Plame’s name first appeared in a July 14, 2003, column by Novak.

The timing could be a critical element in assessing whether classified information was illegally disclosed. If White House aides directed reporters to information that had already been published by Novak, they might not have disclosed classified information.

Fitzgerald is asking questions that suggest he is still trying to assess the accuracy of some of the more serious allegations about administration leaks to reporters other than Novak, according to people involved in the case. Prosecutors have questioned numerous witnesses, some repeatedly, to learn whether two senior White House aides actively peddled Plame’s identity to more than a half-dozen reporters before Novak revealed it in print — an allegation made by an anonymous administration official in a Sept. 28 Washington Post article.

Plame’s name was leaked to reporters “purely and simply for revenge,” the official alleged in the report.

“Prosecutors are interested in the sourcing of that story and whether it’s accurate. If it is not accurate, they would like to know that and move along,” said an attorney for a witness in the case.

This lawyer and two others involved in the case said Fitzgerald has been trying to sort out whether White House officials mounted a campaign to leak Plame’s identity, or whether they were merely spinning information that Novak’s column had already put into the public domain.