WASHINGTON – The evidence prosecutors have assembled in the CIA leak case suggests Vice President Cheney’s chief of staff sought out reporters in the weeks before an undercover operative’s identity was compromised in the news media, casting doubt on one of the White House’s main lines of defense.

For months, the White House and its supporters have argued top presidential aides did not knowingly expose Valerie Plame, the wife of administration critic Joseph Wilson, as a CIA operative. At most, the aides passed on information about her that entered the White House from reporters, the supporters argued.

Special Counsel Patrick Fitzgerald now knows that Cheney aide I. Lewis “Scooter” Libby met three times with a New York Times reporter before the leak of Ms. Plame’s identity, initiated a call to NBC’s Tim Russert and was a confirming source about Mr. Wilson’s wife for a Time magazine reporter.

And in a new twist, a presidential political adviser, Karl Rove, has testified that it’s possible Mr. Libby was his source before Mr. Rove talked to two reporters about the CIA operative.

In light of all the disclosures, “it’s going to be as difficult for the defense to prove the theory that the White House got the information from reporters as it is for Fitzgerald to prove that the White House leaked the information about Mr. Wilson’s wife,” said Washington based white-collar defense attorney James Wareham.

Where Mr. Libby first heard the information still isn’t publicly known, but a full three weeks before Ms. Plame’s name first showed up in print, Mr. Libby was telling New York Times reporter Judith Miller that he thought Mr. Wilson’s wife worked for the CIA, according to Ms. Miller’s testimony.

While Mr. Libby maintains that he didn’t know Ms. Plame’s name until it was published in the news media, the now-public evidence suggests Mr. Libby at least was aware that Mr. Wilson’s wife worked at the CIA and that he spread the information.

Prosecutors must determine whether it was part of an effort to undermine the credibility of Ms. Plame’s husband who was criticizing the White House.

Until this week, “the news media did it” was a standard defense among Republicans trying to protect the Bush administration from the political fallout of Mr. Fitzgerald’s criminal investigation. Loyalists said that even if White House aides had passed on information, they didn’t get it from classified sources and were simply repeating what they heard from journalists.