Heavy volume contributed to technical problems and delays that plagued the rollout Tuesday of the online insurance markets at the heart of President Obama's health care law, according to state and federal officials, who were watching closely for clues to how well the system will work and how many people will take advantage of it.
Many people who tried to compare plans and shop for coverage at healthcare.gov, the federally run exchange that serves as the marketplace for residents of most states, met with messages citing high traffic and advising, "Please wait here until we send you to the login page" or "The system is down at the moment." A state-run exchange in Maryland also posted a message saying it was "experiencing connectivity issues" and asking visitors to try again later.
Speaking at the White House just after 1 p.m., Mr. Obama said that more than a million people had visited the federal site by 7 a.m., more than five times the traffic as on Medicare's Web site. He said his administration would fix technical problems and adjust to "this demand that exceeds anything that we had expected."
States that operate their own enrollment sites reported widely varying levels of traffic, but most said the systems were working, though with some problems caused by having more people than expected go to the exchanges. In the first few hours that their exchanges were operating, New York State's reported two million visits, Kentucky's 24,000, Illinois's more than 62,000 and Connecticut's 14,000. Most of those people were browsing and comparing options; the numbers actually attempting to enroll in an insurance plan was far smaller, and there were more problems reported with that process.
The administration has stressed that consumers could also phone call centers or go in person to social service agencies, which can be found at localhelp.healthcare.gov, that have been designated as "navigators" to help people through the process. But those systems also stumbled out of the gate, dependent on the same computer systems used by people who went online.
At the Spectrum Health Center in West Philadelphia, only a handful of people looking for services arrived Tuesday morning, outnumbered by the people there to help them weigh options and choose one. One consumer, Daniel Flynn, worked with a counselor, Kyle Rouse, but they found that while they could compare plans, they could not get into the system to apply for one.
Mr. Flynn, 28, who has private coverage already, said he learned that through the exchange, "I would potentially pay the same for a plan that's significantly better," with fewer out-of-pocket costs. Another consumer, Roderick Schichtel, who is uninsured, learned that he does not earn enough money to qualify to buy insurance through an exchange, but would qualify for the Medicaid coverage, which was expanded under the health law.
At the Jessie Trice Community Health Center, in a poor section of Miami, out of about 70 people who arrived seeking help with the new program before noon, no one was able to get access to the marketplace. All were given appointments to come back another week.
In Ohio, there were no "navigators" ready to help people on the first day of enrollment, because the state Department of Insurance has not yet authorized any of them.
And in Kentucky, by 9 a.m. the state-run insurance exchange was freezing up, with users unable to take even the first step of creating an account. Gwenda Bond, a spokeswoman, said more than 1,000 applications had been processed online by 9:30 a.m., and that the "high volume of traffic" was to blame for the technical problems.
"This surge of early applications demonstrates the pent-up demand for quality health coverage," Ms. Bond said.
It was unclear to what degree problems with the federal Web sites were due to the kind of technical hurdles that supporters of the program had warned about and that opponents had predicted would demonstrate its unwieldiness. Federal officials conceded Tuesday that even if volume were low, computer problems would be making it hard for people to shop, compare prices and enroll.
Some cybersecurity efforts raised the possibility that the system had been hit by a "denial of service" attack, in which people use linked networks of computers to cause a system to crash by flooding it with traffic.
Tuesday also brought a partial shutdown of the federal government, after the Republican majority in the House said it would pass a bill financing continued operation of the government only if that bill also eliminated money for the Affordable Care Act, known as Obamacare, or delayed its being put into effect for a year. The House has voted more than 40 times to undo all or part of the law, which was passed in 2010.
Striking a defiant tone, Mr. Obama said in his news conference, "They've shut down the government over an ideological crusade to deny affordable health insurance to millions of Americans."
"It is settled and it is here to stay," he said of the law. "And because of its funding sources, it is not impacted by a government shutdown."
But the shutdown did idle some federal employees who had been promoting the expansion of coverage. A White House spokeswoman, contacted about snags in the rollout, said, "Due to the lapse in appropriations, I am not in the office and am not available to answer your message."
Insurance bought through the exchanges by Dec. 15 would take effect on Jan. 1. The open enrollment period runs through March. The 2010 health care law calls for most Americans to have insurance. Those who go without coverage may be subject to tax penalties.
In a point repeated by officials around the country, Gov. Pat Quinn of Illinois, a Democrat who supports the program, said that given the timetable, it would be a mistake to expect a lot to happen on the first day. "What we want folks to do is get educated, and then get enrolled," he said.
Despite months of feverish preparation, officials began the day unsure whether the exchanges had overcome a range of problems, including with Spanish-language versions, subsidy calculators and programs to enroll small businesses.
Nor can officials do more than guess how many people actually will buy private coverage through the exchanges.
The stakes are immense for Mr. Obama, whose signature achievement is the 2010 law that is supposed to push the United States closer to universal health care. Defending the law in the 2012 campaign, he defeated a Republican opponent, Mitt Romney, who vowed to repeal it.
A trouble-plagued launching, accompanied by the complaints of frustrated consumers, could undermine political support for the law, while tepid participation by the uninsured could weaken its financial underpinnings, which depend on the largest possible number of people paying into the system. The logistics of the new online system are daunting, relying on links to government records to verify citizenship and eligibility for subsidies, and to thousands of different coverage combinations
In 34 states, the federal government is entirely or partially running the exchanges, because the states declined to do so.
Correction: October 1, 2013, Tuesday
This article has been revised to reflect the following correction: An earlier version of this article misstated the deadline for enrolling in an insurance plan. It is March 31, not Jan. 1. (Insurance bought through the exchanges by Dec. 15 would take effect on Jan. 1.) The article also misstated the day of an announcement on healthcare.gov, the federally run exchange. It was posted on Tuesday, not on Monday.
This article originally appeared in The New York Times.