In her testimony before a key House committee Wednesday, Health and Human Services Secretary Kathleen Sebelius is expected to acknowledge problems with the HealthCare.gov rollout and pledge quick fixes to the bug-plagued online health insurance marketplace.
"The initial consumer experience of HealthCare.gov has not lived up to the expectations of the American people and is not acceptable," she is expected to say, according to prepared remarks obtained by NBC News. "We are committed to fixing these problems as soon as possible."
Sebelius is expected to to face harsh scrutiny when she appears in front of the House Energy and Commerce Committee. Amid criticism of the health care website's technical glitches, many Republicans have called on Sebelius to resign from her post.
Related: Safe for now? Why Sebelius is unlikely to be axed after Obamacare mess
Sebelius' prepared testimony defends the Affordable Care Act and reassures lawmakers that tech officials are hard at work repairing the website's bugs.
"By enlisting additional technical help, aggressively monitoring errors, testing to prevent new issues from cropping up, and regularly deploying fixes to the site, we are working to ensure consumers' interaction with HealthCare.gov is a positive one, and that the Affordable Care Act fully delivers on its promise," the remarks say.
Her remarks will follow testimony Tuesday from the head of the agency running the embattled federal health insurance website.
Centers for Medicare and Medicaid Services administrator Marilyn Tavenner apologized for the website's issues and vowed once again that they would be rectified.
In testimony before the House Ways and Means Committee, Tavenner also rebutted allegations that the Obama administration misled people about whether they could retain health plans they liked, saying any canceled plans were scrapped by insurers who knew they were not fulfilling the law's requirements.
"This HealthCare.gov site is fixable," she said. "This system is working. It's just not working as smoothly and consistently as we want," she added later.
Officials have promised the website will be fixed by the end of November, giving uninsured Americans two weeks to sign up in time to have insurance by the earliest possible date.
Jeff Zients, the former deputy director of the Office of Management and Budget and Obama's next top economic adviser, has been tapped to help clean up the balky online marketplaces, the administration has said.
Meanwhile, glitches were reported Tuesday night in a Verizon Terremark data center -- which “was experiencing an outage” -- that was impacting the HealthCare.gov marketplace, a U.S. Health and Human Services source told NBC News.
Connecticut’s healthcare exchange, Access Health CT, confirmed the data center outage, the second such incident in three days.
NBC News' Maggie Fox and Jay Blackman contributed to this report.