MIT economist Jonathan Gruber tried to explain and even justify his controversial comments about ObamaCare during a profuse apology on Tuesday before a House committee -- as Rep. Darrell Issa accused him of creating a false model as part of "a pattern of intentional misleading" to get ObamaCare passed. 

Gruber, himself a well-paid consultant during the drafting of the law, was hammered by Republicans on the House oversight committee at his first appearance on Capitol Hill since videos of his remarks surfaced.

Issa, R-Calif., chairman of the House Oversight and Government Reform Committee, also came down hard on Marilyn Tavvener, administrator of the Centers for Medicare and Medicaid Services, who he has accused in the past of allegedly inflating enrollment numbers and “cooking the books.”

Issa told Gruber: “You made a series of troubling statements that were not only an insult to the American people, but revealed a pattern of intentional misleading [of] the public about the true impact and nature of ObamaCare." 

Gruber has come under fire for claiming ObamaCare's authors took advantage of the "stupidity of the American voter." 

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He delivered a mea culpa of sorts in his opening remarks on Tuesday for what he called his "mean and insulting" comments, explaining some of his remarks while trying to take some of them back. After once saying a lack of transparency helped the law pass, Gruber said Tuesday he does not think it was passed in a "non-transparent fashion." 

He also expressed regret for what he called "glib, thoughtless and sometimes downright insulting comments." 

"I sincerely apologize for conjecturing with a tone of expertise and for doing so in such a disparaging fashion," Gruber said. "I knew better. I know better. I'm embarrassed and I'm sorry." 

He said he "behaved badly" but stressed that "my own inexcusable arrogance is not a flaw in the Affordable Care Act." 

Gruber's appearance before the House Oversight and Government Reform Committee Tuesday marked one of Issa's last, high-profile shots at the health care law before he hands over his chairmanship next year. Issa, R-Calif. -- who has led the committee through controversial probes of the Benghazi attacks, the IRS scandal and more -- led the questioning of Gruber, an MIT economist. 

The videos of Gruber's remarks have renewed Republican concerns over the health care law, and the way in which it was drafted and passed. Lawmakers also have obtained videos that show Gruber saying the act was written in a "very tortured way." 

During questioning, Issa asked Gruber, "Are you stupid?" 

"I don't think so, no," he responded. 

Issa added: "So you're a smart man who said some ... really stupid things." 

Rep. Elijah Cummings, D-Md., top Democrat on the committee, also criticized Gruber for giving opponents of the law a "PR gift." 

"You wrapped it up with a bow," Cummings said, while claiming the controversy "has nothing to do with the substance of this issue." 

Issa also slammed the Centers for Medicare and Medicaid Services for allegedly inflating their enrollment numbers. The agency initially claimed enrollment of 7.3 million, but later revised that down to 6.7 million. Issa suggested this was an attempt to "doctor the books" by wrongly including dental plan numbers. The agency called it a mistake. 

Like many congressional hearings, Tuesday's session may provide partisan fireworks without much movement toward changing the law. The president says he will veto any effort to overturn the Affordable Care Act, should such a bill reach his desk after Republicans add Senate control to their House majority next year. 

Gruber has worked as a health care adviser in several states, including to former Massachusetts Gov. Mitt Romney. The federal government paid Gruber nearly $400,000 for his work. 

Also testifying Tuesday was Tavenner. In an effort to distance Tavenner from Gruber's remarks, the administration asked Issa to put her on a different witness panel. They appeared on the same panel on Tuesday. 

The hearing comes as prominent Democrats debate the wisdom of devoting much of 2009 -- Barack Obama's first year as president -- to the bruising battle for the health care legislation, which finally passed without a single Republican vote. Sen. Chuck Schumer of New York is among those Democrats now criticizing the timing. Top liberals are defending Obama, creating new divisions among Democrats right after major losses in this year's elections. 

The Associated Press contributed to this report.