Utah Republican Rep. Jason Chaffetz told the Fox News Channel’s Megyn Kelly on Friday that although a key White House witness in the ill-fated Operation Fast and Furious gun-walking program is willing to testify about what he knows, the Obama administration won’t let him appear before Congress.

White House Counsel Kathryn Ruemmler sent a letter Thursday to Republican lawmakers Rep. Darrell Issa and Sen. Chuck Grassley, refusing their request to speak with Kevin O’Reilly, a former National Security staff member whose emails place him in the middle of the unfolding scandal. Issa and Grassley had written to Ruemmler on March 28, asking the White House to step aside and let O’Reilly talk to investigators.

Grassley is the GOP ranking member on the Senate Judiciary Committee. Issa chairs the House Committee on Oversight and Government Reform, whose members include Chaffetz.

“[O’Reilly’s] personal attorney indicated that he’s more than willing to talk to the committee, on the record, under oath”” Chaffetz told Kelly during her Friday afternoon broadcast. “It is only the White House and the White House Counsel that is saying they will not make him available.” (RELATED: Full coverage of Operation Fast and Furious)

During his time at the White House, records show, O’Reilly carried on an email conversation with Frank Newell, then the head of the Phoenix field office of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). Their emails suggest that Newell was directly briefing O’Reilly on Fast and Furious.

In one email, Newell wrote to O’Reilly, “You didn’t get this from me,” indicating that he may have been subverting the established chain of command within the Department of Justice, which oversees ATF.

In another, Newell said, “Just don’t want ATF HQ to find out, especially since this is what they should be doing (briefing you!).”

Still, Ruemmler refused in her April 5 letter to let Issa, Grassley and their investigators have access to O’Reilly.

“Over six months ago, the White House produced documents responsive to your prior request for communication between Mr. O’Reilly and ATF agent Newell,” she wrote.

“[N]one of these limited communications between Mr. O’Reilly and Mr. Newell revealed the existence of any of the inappropriate investigative tactics at issue in your inquiry, let alone any decisions to allow guns to ‘walk.’”

Ruemmler also cited executive privilege and confidentiality as reasons for denying the lawmakers’ request.

Chaffetz said that the House oversight committee did not receive the emails from the White House, even though the documents were covered by at least one of several subpoenas Congress has issued.

“A brave whistleblower stepped up and gave us these documents,” Chaffetz said on Fox News.

“We have issued twenty-two sets of subpoenas,” Chaffetz added. “For thirteen categories of those subpoenas, the White House has provided zero documents.”

Speaking specifically about the White House’s failure to fully comply with the subpoenas, Chaffetz said, “How dare you? How come you did not provide these documents to the committee when we issued this subpoena? And they unilaterally decided this was not important, which is totally unacceptable.”

“You cannot just ignore subpoenas,” the congressman insisted. “That’s why we are on a collision course where we’ll have to come to the decision to say, ‘are we going to hold the Department of Justice, Eric Holder, in contempt and go through contempt proceedings?’”

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Apr-05-2012 WH Counsel reply on O’Reilly Interview