Washington ? On grand jury audiotapes played at his trial Tuesday, former White House aide I. Lewis Libby said he learned about a CIA officer from Vice President Dick Cheney, forgot it, then learned it again from NBC News reporter Tim Russert a month later.

The complicated history of Libby’s recollections is at the heart of his perjury and obstruction trial in exposing the identity of Valerie Plame, a CIA employee. She is married to war critic and former Ambassador Joseph Wilson.

Libby’s 2004 grand jury testimony – a total of eight hours – conflicts with testimony at his trial by a former White House press secretary, a recent vice presidential spokeswoman, a former CIA official, a former State Department undersecretary and reporters from The New York Times and Time magazine.

All testified that Libby discussed Plame with them. Libby told the grand jury he did not remember Plame coming up in any of those conversations. Special Prosecutor Patrick Fitzgerald has told jurors for weeks that Libby lied. The audiotapes will allow jurors to decide for themselves.

Meanwhile, the long-anticipated testimony by Cheney as well as Libby himself may not materialize. Libby’s lawyers – who two months ago declared they were “calling the vice president” to testify – indicated this week only that Cheney was “potentially” a witness and that Libby might decide against taking the witness stand.

By not testifying during his trial, Libby would avoid cross-examination from Fitzgerald.

In audio tapes from Libby’s grand jury testimony, Fitzgerald can be heard walking Libby through the Bush administration’s response to Wilson’s suggestion in 2003 that the government had twisted prewar intelligence about Iraq.

Libby told the grand jury he was “disturbed … upset’s a fair word I guess” by Wilson’s July 6, 2003, attack on the administration in an op-ed piece in The New York Times.

As for Cheney, “I’m sure he was upset,” Libby added.

To rebut Wilson’s claims, Libby said Cheney told him to leak portions of an intelligence report saying Iraq had “vigorously” tried to acquire uranium from the African nation of Niger. Libby said Cheney assured him that President Bush had authorized the release of the information, which had been classified.

“The vice president instructed me to go talk to Judith Miller to lay things out for her,” Libby said.

Cheney already had told Libby at that point that Wilson’s wife worked for the CIA, a fact that Fitzgerald says Libby relayed to Miller. Libby says he forgot all about Plame until days later, when Russert told him about it.

Russert is expected to testify today and will be a key witness because his recollection of that conversation is at odds with Libby’s.