There was a State Department memo that was circulated on Air Force One back in July '03, that day when the president was flying to Africa. And that memo very clearly was labeled with an X on the lead paragraph that describes...Meaning secret, so it was classified. It was faxed aboard Air Force One by Armitage, the deputy, to Colin Powell. Powell then showed it to Ari Fleischer and to other officials. It was also sent to the White House. So there was a large circle of officials in the National Security Council and on board the plane and back in the White House who had seen that memo and were then aware...

The memo was written because the State Department, undersecretary named Marc Grossman, said, `I'm getting questions from Dick Cheney's office,' from Scooter Libby and from the vice president's office, `about Valerie Plame and Joe Wilson's trip.' And so Marc Grossman goes to the State Department's intelligence official, unnamed, still possibly covert--not sure about that--who had participated in the meetings a year earlier when Wilson and Mrs. Wilson were all talking about the trip over at the agency. He had been the State Department's representative that day at the CIA, and Grossman says, `Write a memo about exactly what happened that day, so that we have something to show the vice president's office.' And so he wrote it out a year later, to the best of his recollection, what Wilson's role was, what Mrs. Wilson's role was. And it's that memo that widened the circulation about the whole thing. ....The State Department agreed with Wilson's description of his findings [of the Niger claim] that it was unambiguously a false report.

As an aside, also interesting is Andrea Mitchell's statement as to her own involvement:

MITCHELL: You know, I should have spoke--'cause there's been a lot blogged about all of this--I was called by the CIA because it was erroneously reported in The Washington Post that I was the recipient of the leak before Novak's column came out, and I had not been. So I was never questioned because I simply told the FBI--and, you know, NBC put out a statement that night--that I had not been a recipient of the leak; in fact, I had learned about it from Novak's column like everyone else. Then after the fact, a lot of us had gotten calls and conversations with people, you know, `Hey, how about the Novak column?' But that was after the fact.

Back to Armitage, the LA Times reported on August 25, 2005:

After a June 12 Washington Post story made reference to the Niger uranium inquiry, Armitage asked intelligence officers in the State Department for more information. He was forwarded a copy of a memo classified "Secret" that included a description of Wilson's trip for the CIA, his findings, a brief description of the origin of the trip and a reference to "Wilson's wife."

The memo was kept in a safe at the State Department along with notes from an analyst who attended the CIA meeting at which Wilson was suggested for the Niger assignment. Those with top security clearance at State, like their counterparts in the White House, had been trained in the rules about classified information. They could not be shared with anyone who did not have the same clearance.

Less than a month later, Wilson went public with his charges. The next day, July 7, this memo and the notes were removed from the safe and forwarded to Powell via a secure fax line to Air Force One. Powell was on the way to Africa with the president, and his aides knew the secretary would be getting questions.

Time Magazine reported on August 8, 2005 (lexis.com):

A source familiar with the memo says neither Powell nor Armitage spoke to the White House about it until after July 6. John McLaughlin, then deputy head of the CIA, confirms that the White House asked about the Wilson trip, but can't remember exactly when.

The AP on July 19, 2005 (lexis.com):

Armitage called Ford after Wilson's op-ed piece in The New York Times and his TV appearance on July 6, 2003 in which he challenged the White House's claim that Iraq had purchased uranium yellowcake from Niger. Armitage asked that Powell, who was traveling to Africa with Bush, be given an account of the Wilson trip, said the former official.

The original June 2003 memo was readdressed to Powell and included a short summary prepared by an analyst who was at a 2002 CIA meeting where Wilson's trip was arranged and was sent in one piece to Powell on Air Force One the next day.