The scrambling underscores the pressures on the administration to fix what is widely viewed as the president's biggest domestic achievement. Millions of Americans have spent countless hours in frustration trying to use the federal Web site, healthcare.gov, and its extensive problems have become a political crisis for the administration, providing new opportunities for Republicans who want to roll back the health care law.
Over the weekend, officials sought to counter pronouncements of failure by announcing that almost half a million people have submitted applications for health insurance through the federal and state marketplaces, about half of them through state exchanges. But officials declined to say how many have actually enrolled in insurance plans, and executives from insurance companies, which receive the enrollment files from the government, say their numbers have been low. The enrollment period ends March 31; those who go without coverage may be subject to fines.
On Monday, Mr. Obama will host a Rose Garden event with people who have successfully enrolled in the health care exchanges. White House aides said he will acknowledge that the technical problems are "inexcusable," but will note, as one adviser said, that the health care law is "more than a Web site."
(Read more: Many try, few succeed on logging into Obamacare exchanges)
"There's great demand for the affordable health care coverage made available by the A.C.A.," Jennifer Palmieri, the White House communications director, said Sunday, referring to the Affordable Care Act. "The challenge for all of us — the state and federal governments and contractors alike — is to make sure the American people can access it simply. We won't rest until they can."
Senior officials took to the Sunday talk shows to defend the Affordable Care Act, and Republicans countered them. Senator Marco Rubio, Republican of Florida, said on "Fox News Sunday" that the early failures do not bode well for the rest of the health care law, adding: "In the 21st century, setting up a Web site where people can go on and buy something is not that complicated."
One major problem slowing repairs, people close to the program say, is that the Centers for Medicare and Medicaid Services, the federal agency in charge of the exchange, is responsible for making sure that the separately designed databases and pieces of software from 55 contractors work together. It is not common for a federal agency to assume that role, and numerous people involved in the project said the agency did not have the expertise to do the job and did not fully understand what it entailed.
The people close to the project spoke on the condition of anonymity because they were not authorized to discuss the system's problems.
Administration officials have been debating whether to designate one or more companies as the quarterback for information technology work on the federal exchange, a complex project that has cost more than $400 million.
(Read more: Obama to call healthcare website glitches 'unacceptable)
Communications between the administration and contractors improved over the weekend as the Centers for Medicare and Medicaid Services began negotiating agreements with contractors on responsibility and deadlines for repairs, people involved in the project say. They hope to have a plan before a Congressional hearing set for Thursday.
"The issue right now is between C.M.S. and the White House," a specialist said Friday before communications improved. "Everybody sits and waits and the meter runs."
A part of the system, hidden from users, draws data from several federal and state databases to determine if consumers qualify for coverage and then calculates the subsidies for which they may be eligible. Another part of the system sends enrollment data to insurers. Several people involved in the project say that problems like those of the last three weeks are not uncommon when software from several companies is combined into a large, complex system.
Insurance executives said in interviews that they were frustrated because they did not know the government's plan or schedule for repairs. Insurers have found that the system provides them with incorrect information about some enrollees, repeatedly enrolls and cancels the enrollments of others, and simply loses the enrollments of still others.