HONOLULU - A December surge propelled health-care sign-ups through the government's rehabilitated website past the million mark, the Obama administration said Sunday, reflecting new vigor for the problem-plagued federal insurance exchange.

Of the more than 1.1 million people now enrolled, nearly a million signed up in December, with the majority coming days before a pre-Christmas deadline for coverage to start in January. Compare that with a paltry 27,000 in October, the federal website's first, error-prone month - or 137,000 in November.

"We experienced a welcome surge in enrollment as millions of Americans seek access to affordable health care coverage," Marilyn Tavenner, head of the Centers for Medicare and Medicaid Services, said in a blog post.

The figures don't represent a full accounting. They don't include December results from the 14 states running their own websites. Overall, states have been signing up more people than the federal government has. But most of that has come from high performers such as California, New York, Washington, Kentucky, and Connecticut. Some states still struggle.

Still, the end-of-year spike suggests that the federal exchange serving 36 states is starting to pull its weight. The windfall comes at a critical moment for President Obama's sweeping health-care law, which becomes "real" for many Americans on Jan. 1 as coverage through the exchanges and key patient protections kick in.

The administration's concern now shifts to keeping the momentum going for sign-ups, and heading off problems that could arise when people who have already enrolled try to use their new insurance.

"They've got the front end of the system working really well," said insurance industry consultant Robert Laszewski. "Now we can move on to the next question: Do people really want to buy this?"

The insurance exchanges - online markets for subsidized private coverage - are still likely to fall short of the administration's targets for 2013. That's a concern because Obama needs millions of mostly younger, healthy Americans to sign up to keep costs low.

Tavenner said fixes to the website, overhauled to address technical problems, contributed to December's figures. But things haven't totally cleared up.

"We have been a little bit behind the curve," acknowledged Rep. Joaquin Castro (D., Texas), whose state has the highest proportion of uninsured residents. Nonetheless, the strong December sign-ups send a message. "The Affordable Care Act is something that's good for the country," said Castro.

"Obamacare is a reality," conceded one of the law's opponents, Rep. Darrell Issa (R., Calif.). As House oversight committee chairman, he has been investigating the rollout problems.