White House officials, fearful that the federal health care website may again be overwhelmed this weekend, have urged their allies to hold back enrollment efforts so the insurance marketplace does not collapse under a crush of new users.
At the same time, administration officials said Tuesday that they had decided not to inaugurate a big health care marketing campaign planned for December out of concern that it might drive too many people to the still-fragile HealthCare.gov.
With a self-imposed deadline for repairs to the website approaching on Saturday, the administration is trying to strike a delicate balance. It is encouraging people to go or return to the website but does not want to create too much demand. It boasts that the website is vastly improved, but does not want to raise expectations that it will work for everyone.
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"We are definitely on track to have a significantly different user experience by the end of this month," Kathleen Sebelius, the secretary of health and human services, said Tuesday. "That was our commitment."
Ms. Sebelius, who supervised development of the troubled website, tried to rally state and local elected officials in a conference call organized by the White House. "I would urge you and your folks on the ground to not hesitate to recommend that people go to HealthCare.gov and get signed up," she said.
Officials said the website was now able to handle 50,000 users at a time, providing enough capacity on a daily basis to enroll millions of people in the next four months.
But those charged with fixing the site worry that 250,000 people might try to use the site simultaneously at times on Saturday and in the days ahead. They say that pent-up demand for insurance in the federal marketplace, combined with a surge of interest among people merely curious about whether it is working, could bring the website to a crawl.
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"Our concern is that we want to make sure that people have the right expectation going into this," said Jennifer Palmieri, the White House communications director. "Early October was a frustrating experience for users. We are preparing for the outcome that we have as many or more visitors as we had on Oct. 1."
About 4.7 million people visited the website on that first day, the administration said.
White House officials offered a similar message on Monday in a meeting with some of their allies, including the Service Employees International Union and Enroll America. Both groups had pledged to work hard to drive traffic to the website.
In the meeting, Ms. Palmieri said, officials urged the groups to hold back, at least for the first several days of December, to see how much traffic the website is getting. Ms. Palmieri summarized the message: "Our recommendation is that we expect there to be really high traffic. You shouldn't be driving traffic."
If the website again crashes repeatedly, Mr. Obama's critics are sure to pounce and some of his Democratic allies may become anxious and apprehensive. Since the website went live eight weeks ago, the botched system has become a symbol of what Republicans say is an overreaching, incompetent federal government. The debate about the website's failures, and the broader role of government, may shape the outcome of next year's congressional elections.
Aides to Mr. Obama have spent the last several days trying to manage expectations by offering high estimates of potential traffic at the end of the month, and by acknowledging that the system will still have problems in the weeks ahead.
"The system will not work perfectly," Jeffrey D. Zients, who took over management of the website repair effort, told reporters on Friday. He said the site would be able to handle 50,000 users, but added, "To be clear, there will be times that volume on HealthCare.gov will exceed this capacity."