Medicare Administrator Marilyn Tavenner did not give House Ways and Means Committee Chairman Dave Camp (R-Mich.) numbers on enrollment in the Affordable Care Act, despite his persistant questioning. (The Washington Post)

The Obama administration official directly responsible for the troubled rollout of the federal health insurance Web site apologized Tuesday, promising to fix problems that have prevented many consumers from signing up for coverage under President Obama’s health-care law.

Marilyn Tavenner, administrator of the Centers for Medicare and Medicaid Services, also defended her agency’s management of the project and blamed some of the setbacks on the main contractor, Fairfax-based CGI Federal.

Tavenner is the first administration official to testify publicly about the problems plaguing the Web site that supports the health law. She told members of the House Ways and Means Committee that the site is working, though not as well or as fast as officials would like. She said technology experts are working diligently on it and that it will steadily improve before it is completely fixed by the end of November.

Tavenner’s remarks served as something of a warm-up for a session scheduled for Wednesday featuring Health and Human Services Secretary Kathleen Sebelius, the administration’s top health official.

House Republicans have been anxious to grill Sebelius and other administration officials about their roles in the botched debut of, the main conduit for people in 36 states to browse and buy health insurance under the health-care law. Starting next year, most Americans will have to carry health insurance or face a fine.

Marilyn Tavenner, administrator of the Centers for Medicare & Medicaid Services, apologized to Americans who had trouble using during her testimony at a hearing of the House Ways and Means committee Tuesday. (The Washington Post)

The Web site froze shortly after its Oct. 1 launch. Although some of the initial problems have been addressed, serious bugs have surfaced in the weeks since then. Officials have said it will take until the end of November to ensure that the site works properly for most people.

“To the millions of Americans who have attempted to use to shop and enroll in health-care coverage, I want to apologize to you that the Web site has not worked as well as it should,” Tavenner said. “We know how desperately you need affordable coverage.”

Republicans on the committee asked pointed questions but were relatively gentle with Tavenner, a former Virginia health secretary who is popular with figures in both parties. A political appointee, she was the first CMS head to be confirmed by the Senate in more than a decade.

Sebelius will probably get rougher treatment Wednesday, when she appears before the House Energy and Commerce Committee. Some Republicans have called for her resignation, including Sen. Lamar Alexander (Tenn.), the top Republican on the Senate health panel, who made his views known Tuesday.

Tavenner’s agency, which is part of the Department of Health and Human Services, has a $1 trillion annual budget. CMS officials administer Medicare and Medicaid and are in charge of implementing the Affordable Care Act, the law widely referred to as Obamacare.

In the wake of the Web site’s troubles, many critics blamed CMS for poorly managing the project. The agency’s job included coordinating and testing the work of 55 contractors.

Executives with two of those private firms — including a senior vice president at CGI Federal — testified before the House Energy and Commerce Committee last week that the agency did not fully test the site until two weeks before the launch. Ideally, such testing would have been done months in advance, they said.

During the Tuesday hearing, Tavenner rejected the allegation that the CMS mishandled the health-care project, adding that the agency has successfully managed other big initiatives. She said the site and its components underwent continuous testing but erred in underestimating the crush of people who would try to get onto the site in its early days.

“In retrospect, we could have done more about load testing,” she said.

Under questioning, Tavenner pointed the finger at CGI Federal, saying the company sometimes missed deadlines. “We’ve had some issues with timing of delivery,” she said.

The hearing provided a forum for lawmakers on both sides of the aisle to talk about the health-care law. Democrats noted the irony that Republicans, whose opposition to the law contributed to a temporary government shutdown this fall, are now complaining that not enough people have been able to participate in the program.

“It doesn’t pass the laugh test that they somehow care about getting this right,” Rep. Joseph Crowley (D-N.Y.) said.

Republicans hammered on a range of issues, including recent reports that hundreds of thousands of people who own private insurance are having their policies terminated. The health law requires plans to cover certain basic benefits starting next year; most plans that do not are being discontinued Dec. 31.

They say the terminations contradict assertions by Obama, made as far back as 2009, that under the health-care overhaul, people would be able to keep their insurance if they liked it.

“Can you understand at least the level of frustration based on the claim of the president of the United States that people were going to be able to keep what they had, and it’s not turning out to be true as they understood that statement?” Rep. Peter Roskam (R-Ill.) asked Tavenner.

Tavenner said that the cancellation letters did not result from the law, but rather from decisions made by insurance companies.