Todd Park, President Obama’s top technology adviser, said the failure occurred in the part of the Web site that lets people create user accounts at the beginning of the insurance sign-up process. The crash prevented many people from viewing any of their insurance options or gaining access to information on what federal subsidies might be available.

“At lower volumes, it would work fine,” Mr. Park said of the Web site, healthcare.gov. “At higher volumes, it has problems.”…

Mr. Chopra noted that when United Airlines and Continental merged their online reservations systems, it took weeks to iron out problems.

“This is par for the course for large-scale I.T. projects,” Mr. Chopra said. “We wish we could launch bug-free, but in reality that’s not that easy to do. The reality is that if you have a product that people want, people will tolerate glitches because they expect them.”