Prosecutors investigating whether White House officials illegally leaked the identity of Wilson's wife, a CIA officer who had worked undercover, have been told that Bush's top political strategist, Karl Rove, and I. Lewis Libby, chief of staff for Vice President Dick Cheney, were especially intent on undercutting Wilson's credibility, according to a person familiar with the inquiry.

While lower-level White House staff members typically handle most contacts with the media, Rove and Libby began personally communicating with reporters about Wilson, prosecutors were told.

A source directly familiar with information provided to prosecutors said Rove's interest was so strong that it prompted questions in the White House. When asked at one point why he was pursuing the diplomat so aggressively, Rove responded: "He's a Democrat." Rove then cited Wilson's campaign donations, which leaned toward Democrats, the person familiar with the case said.

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Activities aboard Air Force One are also of interest to prosecutors -- including the possible distribution of a State Department memo that mentioned Wilson's wife. Prosecutors are seeking to find out whether anyone who saw the memo learned Plame's identity and passed the information to journalists. Telephone logs from the presidential aircraft have been subpoenaed; among those aboard was former White House press secretary Ari Fleischer, who has testified before the grand jury.

The source familiar with the investigation said Saturday that prosecutors had obtained a White House call sheet showing that Novak left a message for Fleischer on the afternoon of July 7, 2003, the day after Wilson's op-ed article appeared and the day that Fleischer left with the president for Africa. Fleischer declined to comment for this article, but has flatly denied that he was the source of the leak.

Wilson said in an interview Saturday that he had known that Novak was interested in him a week or so before the column appeared. He said that a friend who saw Novak on the street reported that Novak told him, "Wilson is an (expletive) and his wife works for the CIA."

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There have been other indications of a concerted White House action against the former envoy. Washington Post reporter Walter Pincus has said that two days before Novak's column, he was told by an "administration official" that the White House was not putting much stock in the Wilson trip to Africa because it was "set up as a boondoggle by his wife, an analyst with the agency working on weapons of mass destruction," according to an account of the conversation Pincus wrote for the Summer 2005 issue of Nieman Reports, published by the Nieman Foundation for Journalism at Harvard University.