White House spokesman Jay Carney said the performance of the troubled HealthCare.gov website was significantly improved and the site had logged 375,000 visitors on Monday by noon.
Carney said the website had made significant strides in implementing improvements by a Nov. 30 deadline, but that President Barack Obama believed there was more work to be done to make it function more smoothly.
The troubled website showed some signs of stress with the crush of visitors on Monday. It temporarily directed visitors in some states to a waiting page, saying there were "a lot of visitors right now."
Officials have said the page would be deployed as part of new queuing system when traffic surpassed capacity. A check by Reuters showed visitors waiting for the Florida, Pennsylvania and South Carolina markets. But the queue in Pennsylvania and South Carolina quickly disappeared as volumes fluctuated.
The Department of Health and Human Services confirmed that the queuing system was deployed for the 36 states served by HealthCare.gov.
Beyond immediate capacity issues, officials are still scrambling to repair and install functions at the crucial "back end" of the system that are needed to finalize enrollments with insurers.
"The real challenges remain, and that's downstream," said Rick Howard, research director for the technology consultant Gartner. "The real error rate will be in the billing transactions and how accurate the billing information is and how accurate the premium calculation is."
The administration said it will refocus attention on those issues this week by holding meetings with insurers and state healthcare officials among other participants in Obama's landmark healthcare overhaul to discuss efforts to nail down functions for handling insurance payments including federal subsidies for consumers.
Without those functions working properly, HealthCare.gov and websites for 14 state-run marketplaces could have difficulty operating in 2014.
The president is under pressure to get the botched Oct. 1 rollout of the Patient Protection and Affordable Care Act, commonly known as Obamacare, back on track after a series of technical problems. The rocky debut of Obama's signature legislative achievement has become a major political embarrassment, while emboldening his Republican rivals seeking to dismantle the law, and frustrating his fellow Democrats who worry Obamacare will damage their reelection bids.
Networks of volunteer organizations resumed enrollment activities after the Thanksgiving holiday long weekend, many of them with backlogs of would-be applicants waiting for access.
Jeffrey Zients, the Obama aide charged with fixing the site, said that while HealthCare.gov had improved, he warned the public that peak traffic volumes during the coming weeks could overwhelm it as consumers scramble to sign up before the Dec. 23 deadline.
In a sign of increasing enrollment volumes, preliminary government data showed about 100,000 people choosing a health plan through HealthCare.gov during the month of November, as officials and tech experts worked at a frenzied pace to improve the site's capacity, according to a source familiar with the issue.
That early figure was nearly four times the 27,000 plan selections reported for October, the first month the exchanges were open. But it is still far short of the administration's projection in September that nearly 500,000 people would sign up through the insurance marketplaces in the first month, according to documents obtained by congressional investigators.
Official November data will be released in two weeks.
Ultimately, 7 million Americans were expected to sign up for private health insurance offered through the online marketplaces for 2014, according to the Congressional Budget Office.
Groups helping consumers enroll in Obamacare coverage say they are encouraged by the improved performance of HealthCare.gov and are starting new efforts to reach consumers.
AIDS Alabama, a statewide non-profit organization that received a federal grant to help people enroll, had been relying largely on paper applications to sign people up until last week, when they noticed major improvement in the website, said Lauren Banks, the organization's director of policy and advocacy.
Banks said the website was still not working perfectly - the organization noticed a glitch last week that seemed to produce incorrect information about tax subsidies.
Despite some lingering issues, Banks said the organization planned a radio campaign to get people enrolled by Dec. 23 so they could have coverage starting next year.
Enroll America, the nonprofit group that serves as a flagship for private sector enrollment efforts under Obama's landmark healthcare law, will launch a new "Coverage is Coming" push this week, with more than 1,000 events over the next three weeks ranging from commemorations of World AIDS Day to community health summits and holiday toy drives, according to Enroll America spokesman Justin Nisly.
The groups are particularly focusing their efforts on young enrollees. The administration has said it needs a large portion of young and healthy Americans to enroll to offset the cost of sicker beneficiaries and keep Obamacare financially viable.
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