Vice President Dick Cheney's spokeswoman testified Thursday that she told Cheney and his chief of staff, I. Lewis "Scooter" Libby, that a prominent war critic's wife worked for the CIA days before Libby said he learned it from a reporter.

Cathie Martin's testimony during the third day of Libby's perjury trial described Cheney's personal eagerness to refute war criticism by former ambassador Joseph Wilson in 2003. Wilson claimed Cheney's office sent him on a fact-finding mission that questioned intelligence President Bush later relied on to go to war.

Wilson's wife, CIA operative Valerie Plame, actually conceived the idea for the trip, witnesses have testified. Special Prosecutor Patrick Fitzgerald is trying to show that Cheney's office wanted to make that clear to reporters.

Fitzgerald says Libby learned that fact on several occasions and discussed it with reporters as part of the White House effort to discredit Wilson. When FBI agents began investigating the leak of Plame's identity, Libby lied and said he only learned about Plame from reporters, Fitzgerald said. Libby is on trial on perjury and obstruction charges.

Martin is the fourth person to describe conversations with Libby about Plame and demonstrated the best recollection of the group. She is also the closest witness to Cheney's inner circle. Defense attorneys, who were to question her later Thursday, have used cross-examination of other witnesses to highlight memory flaws.

Martin said that Wilson's criticism was a direct attack on the president's credibility. Wilson says he debunked claims that Iraq was trying to buy uranium from Niger long before that statement ended up in the 2003 State of the Union speech.

Cheney and Libby were eager to refute that, Martin said. She described calling a CIA spokesman to figure out the genesis of the mission.

"We didn't send him," Martin recalled saying. "If we didn't send him, you must've sent him. Who sent him?"

That's when Martin said the CIA spokesman told her that Wilson's wife worked for the CIA. She said she immediately told Cheney and Libby about it. She couldn't pinpoint the date of the conversation but said it definitely took place no later than July 6. Libby says he learned Plame's identity days later.

Cheney took a personal interest in the issue, Martin said, and in the following days dictated media "talking points" making it clear that his office was not responsible for the Wilson trip.

The talking points do not refer to Plame and nobody has been charged with leaking her identity.

Libby says he did not lie about how he learned about Plame, but rather honestly forgot.