But he said that he was unaware that the federal online marketplace, healthcare.gov, was riddled with technological flaws before it went live on Oct. 1. "I was not informed directly that the website was not working the way it was supposed to," he said.

The president said the website would be working better by Nov. 30, the administration's self-imposed deadline to fix it, but added, "It is not possible for me to guarantee that 100 percent of the people 100 percent of the time will have a perfectly seamless and smooth experience."

Obama said he understood why consumers who received cancellation notices from insurers were upset. "It's scary," he said. But he also encouraged them to look at better insurance options on the new marketplace where some also may qualify for subsidies.

The president also took a far more sober tone than he had in the past about the difficulties involved in buying insurance. "Buying health insurance is never going to be like buying a song on iTunes," he said, noting the complexities of comparing insurance plans. In the months preceding the rollout of the new law, Obama repeatedly compared the process to using websites such as Amazon or Kayak.

White House officials said Thursday that new plans sold next year would still have to offer the new benefits, which include hospitalizations, mental health services and maternity coverage.

But the officials said insurers would be free to offer their customers the option to remain on their current plans rather than switching to the new plans, which in some cases are more expensive.

If insurers offer this option, however, they would be required to notify consumers which benefits their current plans are missing. Insurers would also have to alert their customers that other options might be available on the new marketplaces created by the Affordable Care Act.

It is unclear how many insurers would opt to extend current plans. Industry officials have said that such extensions would be burdensome.

The White House move, which officials characterized as a "transition," would not allow health insurers to sell current plans to new customers next year. House Republicans have been pushing for this, which most health experts believe would effectively destroy the new marketplaces created by the health law.

The president was under intense pressure from Democrats on Capitol Hill to find a fix. Democratic unity crumbled as lawmakers were pounded by their constituents over the rocky rollout of Obamacare, especially as many members begin tough re-election battles.

House Democrats have increasingly threatened to support a Republican plan due for a vote today that would allow insurers to continue to offer plans that don't meet new standards in the health care law. Democratic senators have offered their own legislation.

Baltimore Sun reporter Meredith Cohn and Tribune Washington Bureau reporters Noam N. Levey, David Lauter, Lisa Mascaro and Michael A. Memoli contributed to this article.