WASHINGTON » Defending President Barack Obama’s much-maligned health care overhaul in Congress, his top health official was confronted today with a government memo raising new security concerns about the trouble-prone website that consumers are using to enroll.

The document, obtained by The Associated Press, shows that administration officials at the Centers for Medicare and Medicaid Services were concerned that a lack of testing posed a potentially "high" security risk for the HealthCare.gov website serving 36 states. It was granted a temporary security certificate so it could operate.

Security issues are a new concern for the troubled HealthCare.gov website. If they cannot be resolved, they could prove to be more serious than the long list of technical problems the administration is trying to address.

"You accepted a risk on behalf of every user…that put their personal financial information at risk," Rep. Mike Rogers, R-Mich., told Health and Human Services Secretary Kathleen Sebelius during questioning before the House Energy and Commerce Committee. "Amazon would never do this. ProFlowers would never do this. Kayak would never do this. This is completely an unacceptable level of security."

Sebelius countered that the system is secure, even though the site has a temporary certificate, known in government parlance as an "authority to operate." Sebelius said a permanent certificate will only be issued once all security issues are addressed.

Added spokeswoman Joanne Peters: "When consumers fill out their online…applications, they can trust that the information they’re providing is protected by stringent security standards and that the technology underlying the application process has been tested and is secure. Security testing happens on an ongoing basis using industry best practices."

A security certificate is required before any government computer system can process, store or transmit agency data. Temporary certificates are allowable, but under specific circumstances.

Earlier, the secretary said she’s responsible for the "debacle" of cascading problems that overwhelmed the government website intended to make shopping for health insurance clear and simple.

"Hold me accountable for the debacle," Sebelius said during a contentious hearing. "I’m responsible."

Sebelius is promising to have the problems fixed by Nov. 30, even as Republicans opposed to Obama’s health care law are calling in chorus for her resignation. She told the committee that the technical issues that led to frozen screens and error messages are being cleared up on a daily basis.

Addressing consumers, Sebelius added, "So let me say directly to these Americans, you deserve better. I apologize."

The Sept. 27 memo to Medicare chief Marylin Tavenner said a website contractor wasn’t able to test all the security controls in one complete version of the system.

"From a security perspective, the aspects of the system that were not tested due to the ongoing development, exposed a level of uncertainty that can be deemed as a high risk for the (website)," the memo said.

It recommended setting up a security team to address risks, conduct daily tests, and a full security test within two to three months of going live.

HealthCare.gov was intended to be the online gateway to coverage for millions of uninsured Americans, as well those who purchase their policies individually. Many people in the latter group will have to get new insurance next year, because their policies do not meet the standards of the new law.

Sebelius’ forthright statement about her ultimate accountability came as she was being peppered with questions by Rep. Marsha Blackburn, R-Tenn., about who was responsible. It was Blackburn who introduced the term "debacle."

Rep. Henry Waxman of California, the ranking Democrat on the committee, scoffed at Republican "oversight" of a law they have repeatedly tried to repeal.

"I would urge my colleagues to stop hyperventilating," said Waxman. "The problems with HealthCare.gov are unfortunate and we should investigate them, but they will be fixed. And then every American will have — finally have access to affordable health insurance."

Throughout the 3-hour hearing, Sebelius was respectful and poised, often addressing lawmakers as "sir" or "congresswoman." She kept her cool as some lawmakers repeatedly cut off her answers. But she did not shy a few times from tersely interjecting her views while a member was speaking.

The standing-room-only hearing room was silent when she swore an oath to tell the truth and began her statement. "I apologize," she told the rapt committee.

Sebelius faced questions about problems with the website as well as a wave of cancellation notices hitting individuals and small businesses who buy their own insurance.

Lawmakers also want to know how many people have enrolled in plans through the health exchanges, a number the Obama administration has so far refused to divulge, instead promising to release it in mid-November.

On Tuesday, Medicare chief Marilyn Tavenner was questioned for nearly three hours by members of the House Ways and Means Committee who wanted to know why so many of their constituents were getting cancellation notices from their insurance companies.

The cancellations problem goes to one of Obama’s earliest promises about the health law: You can keep your plan if you like it. The promise dates back to June 2009, when Congress was starting to grapple with overhauling the health care system to cover uninsured Americans.

As early as last spring, state insurance commissioners started giving insurers the option of canceling existing individual plans for 2014, because the coverage required under Obama’s law is significantly more robust. Some states directed insurers to issue cancellations. Large employer plans covering most workers and their families are unlikely to be affected.

The law includes a complicated "grandfathering" system to try to make good on Obama’s pledge. It shields plans from the law’s requirements provided the plans themselves change very little. Insurers say it has proven impractical. The cancellation notices are now reaching policyholders.

Tavenner blamed insurance companies for cancelling the policies and said most people who lose coverage will be able to find better replacement plans in the health insurance exchanges, in some cases for less money.