Pablo Martinez Monsivais / AP President Barack Obama, accompanied by Health and Human Services Secretary Kathleen Sebelius, announces a revamped contraception policy on Feb. 10, 2012, in Washington

Updated at 4:00 p.m., Oct. 29 to include Sebelius testimony

The head of the government agency in charge of implementing a major insurance web site at the center of Affordable Care Act apologized Tuesday for bungling its rollout and said she expected the software behind it to perform better.

“I want to apologize to you…We know how desperate you are for affordable coverage,” said Marilyn Tavenner, head of the Centers for Medicare and Medicaid Services (CMS) when she appeared before the House Ways and Means Committee Tuesday morning. Asked if pre-launch testing of the web site, Healthcare.gov, showed the site was destined to operate poorly, Tavenner said, “We were comfortable with its performance.”

Government contractors that appeared before a different House committee last week implied that systems tests run before Healthcare.gov’s debut indicated it had serious problems. Tavenner, echoing an explanation for the web site problems offered by other Obama Administration officials, including the President, said web traffic simply overwhelmed the system. Information technology consultants who have examined the web site have said, however, that bad software code within the site caused it to function poorly.

One day before U.S. Health and Human Services Secretary Kathleen Sebelius is set to testify before Congress, Tavenner’s appearance offered lawmakers a chance to grill the CMS administrator on the specifics of planning and building Healthcare.gov. For the most part, members of the House committee let this opportunity pass without delving into the details of the government procurement process and the management of the contractors hired to design the website. Instead, most Democratic lawmakers used their designated question time to tout the virtues of the ACA, while their Republican counterparts criticized the law itself. CGI, the lead contractor responsible for building the website, was not even mentioned until the hearing approached the two-hour mark. Some lawmakers on Tuesday asked no questions at all, instead preferring to rail against political opponents and read letters from constituents that supported their positions.

There were a few exceptions. Texas Republican Reps. Kenny Marchant and Kevin Brady both raised an emerging and troubling issue for consumers. Many of those who currently purchase coverage in the individual market are receiving letters from insurers canceling policies at the end of 2013 that do not comply with the ACA’s new regulations. These consumers can sign up for new ACA-compliant policies, but have little time. CMS has said healthcare.gov, responsible for handling individual market enrollment in 36 states, will operate smoothly and efficiently by the end of November. Consumers shopping in this market must purchase insurance plans by Dec. 15 to enroll in a policy beginning Jan. 1. Those who have insurance now and do not, or cannot, sign up in that short two-week period could experience a gap in coverage, particularly concerning for those with ongoing health conditions. “My constituents are frightened,” said Brady.

Wisconsin Rep. Paul Ryan, the Republican Party’s vice presidential nominee in 2012, said he was concerned that Healthcare.gov’s enrollment process may allow some Americans to apply for and receive federal insurance subsidies they are not legally entitled to. These consumers, Ryan said, could face a “rude awakening” in several years when the government tries to recoup these funds through income tax filings. And several Democratic lawmakers seemed particularly frustrated that Americans trying to purchase regulated and subsidized insurance plans were stymied by a dysfunctional web site that is at the center of a law they helped pass.

“The fact is the Administration really failed these Americans,” said Pennsylvania Rep. Allyson Schwartz, a Democrat. She called the problematic rollout of Healthcare.gov “inexcuseable and unacceptable.” Texas Rep. Lloyd Doggett, another Democrat, said, “The promise of affordable health care can…be destroyed by problems of management.” He said he wanted more information on an ACA program that trains and hires consumer assistance workers to help those signing up for coverage, demanding that Tavenner provide progress reports on this program ahead of schedule.

When Sebelius faces lawmakers on Wednesday, she is likely to field more pointed questions about what role she played in building and rollout of Healthcare.gov. Several Republicans in Congress have called for her resignation, but Administration officials have said she has the full confidence of President Obama. According to her prepared testimony, Sebelius will acknowledge that healthcare.gov has not performed well since its launch and that the Administration is working hard to improve the site’s performance. Her advance remarks, which are nearly identical to testimony read by Tavenner on Tuesday, offer no new details on the reasons for the site’s bungled rollout, including the lack of sufficiently rigorous pre-launch testing.