Secretary of Health and Human Services Kathleen Sebelius said officials are working "24/7" to improve the government's health insurance website.
Nevertheless, calls for her resignation continue.
But Sebelius fired back at her critics, saying, "The majority of people calling for me to resign I would say are people who I don't work for and who do not want this program to work in the first place."
"I have had frequent conversations with the president," she continued. "And I've committed to him that my role is to get the program up and running and we will do just that."
Her remarks come after a hearing Thursday before the U.S. House Energy and Commerce Committee in which both Democrats and Republicans denounced the government's roll-out of HealthCare.gov.
"This is unacceptable. It needs to be fixed," Rep. John Dingell, D-Mich., said.
Rep. Anna Eschoo, D-Calif., said, "Amazon and eBay don't crash the week before Christmas."
"How can the administration punish innocent Americans by forcing them to buy from a system that doesn't work and whose roll-out has been nothing short of a disaster?" Rep. Fred Upton, R-Mich., asked.
Republicans on the committee accused the administration of misleading Congress prior to the roll-out.
"We were repeatedly told by members of the administration that everything would be working properly and it would all be done on time," Rep. Marsha Blackburn, R-Tenn., said.
Software contractors who worked on the website said they'd done their part, insisting the administration did not allow enough time for developing or testing the site.
Meanwhile, Sebelius said she's calling up the reserves, hoping for a quick fix to an ailing system.
"We've looked across the federal government at some of the best tech experts who were not necessarily on the ground working on this project but are now involved," Sebelius said.
Some Democrats are saying the administration should extend the deadline for signing up and revise the penalties for those who don't enroll.
Another worry: It's now clear that many Americans are finding their health insurance premiums have shot up.
And Kaiser Health News reported that hundreds of thousands have received cancellation notices despite the president's original promise that people could keep their plans.
Democrats who thought they'd run for re-election next year, touting the success of Obamacare, are beginning to worry about political fall-out.
"I'm also concerned about what happens next," Upton said. "Will enrollment glitches become provider payment glitches? Will patients show up at their doctors' offices or the hospital to be told that they aren't covered or even in the system?"
Sebelius will appear before the House Energy Committee next Wednesday.