Washington (CNN) -- The chairman of the House Judiciary Committee called Tuesday for the appointment of a special counsel to investigate whether Attorney General Eric Holder was honest when he testified earlier this year about his knowledge of a now-discredited federal gunrunning operation.
"Allegations that senior Justice Department officials may have intentionally misled Members of Congress are extremely troubling and must be addressed by an independent and objective special counsel," Rep. Lamar Smith, R-Texas, wrote in a letter to President Barack Obama.
Documents leaked on Capitol Hill to CNN and other news organizations purport to show that Holder knew about "Operation Fast and Furious" earlier than indicated when he testified before the Judiciary Committee in May.
The operation involved agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives allowing illegal sales of guns believed to be destined for Mexican drug cartels to "walk" from Phoenix, Arizona, gun stores into Mexico.
The idea was to track the sellers and purchasers of guns to Mexican cartels, but the program became mired in controversy after weapons found at Mexican and American murder scenes were traced back to the program. Mexican officials and critics in the U.S. called the program a failure, saying it exacerbated the longstanding problem of U.S. weapons getting into the hands of the violent Mexican cartels.
Sen. Charles Grassley, R-Iowa, ranking member on the Judiciary Committee, told CNN that Holder knew of the operation as early as January.
"He knew it on January 31, when he came to my office for other discussions. I handed him a letter, asking for a lot of documents, and I was beginning my investigation of Fast and Furious. So that's several months back before he said he knew about it. So right there, he is wrong and misleading," Grassley said.
The question of who knew what and when about the program has been central in the minds of critics.
At the committee's May 3 hearing, Rep. Darrell Issa, R-California, raised the subject of the program with Holder.
"When did you first know about the program, officially, I believe, called Fast and Furious? To the best of your knowledge, what date?" Issa asked.
"I'm not sure of the exact date, but I probably heard about Operation Fast and Furious for the first time over the past few weeks," Holder testified.
While Smith focused on Holder's May 3 appearance, the attorney general also told Sen. Kay Bailey Hutchison, R-Texas, on March 10 that he had recently learned of "concerns" about the program.
"It is true there have been concerns expressed by ATF agents about the way in which this operation was conducted, and I took those allegations, those concerns, very seriously and asked the inspector general to try to get to the bottom of it," Holder said at the time.
A July 5, 2010, memo from the director of the National Drug Intelligence Center to Holder mentions the operation. But the memo does not appear to contain any of the controversial tactics employed in it.
The Justice Department insists Holder has not wavered in his contention that he did not know details of the operation, including the controversial tactic of ATF agents allowing guns to "walk."
"The attorney general has consistently said he became aware of the concerning tactics earlier this year, and when he did, he asked the (inspector general) to investigate," a senior Justice official told CNN.
The official said the leaked documents -- including the July 2010 memo -- are bits of brief headlines that the attorney general receives daily, and are not "briefings" on specific subjects. The official said Holder did not receive information about the tactics employed by the ATF at any point last year.
Issa, who is chairman of the House Oversight and Government Reform Committee, "should be familiar with the difference between knowing about an investigation and being aware of questionable tactics employed in that investigation," the official said. "Documents provided to his committee show he was given a briefing that included the Fast and Furious operation in 2010 -- a year before the controversy emerged."
The issue blew up in December when Border Patrol Agent Brian Terry was killed and two guns from the operation were found at the scene.
Emotions were also inflamed in Mexico, where the episode seemed to justify longstanding claims that the U.S. complained about drugs flowing north while not controlling the southbound flow of weapons.
One e-mail exchange between two officials referred to guns "walking," but there is no indication that Holder saw the memo. The October memo to Jason Weinstein in the Criminal Division says, "I don't know how much grief we get for gun walking."
The Justice official said the gun walking referred to in that memo was part of a separate ATF operation that was handled out of Tucson, and had begun in 2007, before Holder took office.
During a televised Justice Department news conference last month, Holder acknowledged the ATF's gunrunning operation "was clearly a flawed enforcement effort" but said ongoing investigations will find that involvement did not reach "the upper levels" of the Justice Department.
The Justice Department and Issa's committee are already investigating the case. Both are expected to continue for several more months.
CNN's Jim Barnett, Alan Silverleib, Deirdre Walsh and Michael Martinez contributed to this report.