Two months after the troubled launch of its signature health care initiative, the Obama administration on Sunday announced that its online insurance marketplace now functions smoothly for the "vast majority" of consumers seeking to shop for and enroll in coverage.

"We've doubled the system's capacity and HealthCare.gov can now support its intended volume," said Jeff Zients, the administration official overseeing repairs to the system, on a conference call with reporters today.

The website can handle 50,000 concurrent users and 800,000 users per day, Zients said, marking a significant improvement from October when it crashed under the weight of just several thousand visitors. The site's response time and error rate for applicants have also vastly improved, he said.

"In effect, we have widened the system's on-ramp. It now has four lanes, instead of two," Zients said of the account registration process, which had been a major bottleneck for consumers in early October.

The announcement kicks off an effort by the White House to rebound from an embarrassing and politically bruising eight week stretch that has taken a significant toll on President Obama's poll numbers and credibility. Officials hope a vastly improved website will begin to rebuild confidence in the Affordable Care Act and reassure nervous congressional Democrats facing reelection next year.

A report released by the Department of Health and Human Services says the marketplace, which was down roughly 60 percent of the time in October, is now much more stable. As of late November, it was accessible and available daily more than 90 percent of the time, on average, officials said.

Today "is not a magic moment but a process of continual improvement over time," said Julie Bataille, communications director for the Centers for Medicare and Medicaid Services, which manages the website.

The report identifies as root causes of the problems "hundreds of software bugs, insufficient hardware and infrastructure." It says technical teams have implemented 400 fixes, with more than 300 coming online in the last three weeks.

"We now believe the HealthCare.gov site works for the vast majority of users," Bataille said. The administration has defined "vast majority" as 80 percent of consumers looking to enroll online.

Still, significant problems persist with the system.

The report implies that the website continues to experience unscheduled outages at least 5 percent of the time, and officials signaled that there are still concerns about slow-downs during high traffic periods.

HHS Secretary Kathleen Sebelius advised consumers in a blog post Saturday to visit the site at off-peak times - mornings, nights and weekends - to avoid delays and potential congestion. Officials said today they are not yet ready to begin aggressively summoning people to the site until it's demonstrated to be stable.

"The door is open for new consumers and we invite them in," said Bataille, "But our focus is on making sure that those who have tried to enroll in the past several weeks complete that process."

Insurers continue to complain about unreliable data on applicants which they receive from the site. And the administration has not yet completed building the electronic payment system that will transfer government subsidies to insurance companies to help cover the cost of plans.

The new report also renews questions about the administration's management of the project and why many of the touted "fixes" weren't in place to begin with, including 24/7 "technical monitoring systems" and daily meetings about the site's progress.

HHS concluded that the website was "fixable but only by significant changes to the management approach and a relentless focus on execution," highlighting some serious shortcomings in those areas from the beginning.

The report also undermines the administration's early explanation that unexpected heavy volume to HealthCare.gov was largely responsible for the outages consumers faced. The culprit turns out to have been significant software and hardware glitches.

"There is more work to be done to continue to improve and enhance the website and continue to improve the consumer experience in the weeks and months ahead," the report says. "While we strive to innovate and improve our outreach and systems for reaching consumers, we believe we have met the goal of having a system that will work smoothly for the vast majority of users."