CHICAGO -- The Obama administration extended Monday's deadline for signing up for health insurance by a day, giving Americans in 36 states more time to select a plan.

It was the latest in a series of pushed-back deadlines and delays that have marked the rollout of the health care law, the signature legislative achievement of Obama's first term.

President Barack Obama himself signed up for coverage through the government site over the weekend -- a purely symbolic move since he will continue to get health care through the military as commander in chief. He chose a less-expensive "bronze" plan.

Julie Bataille, a spokeswoman for the federal agency in charge of the overhaul, said the grace period -- which runs through Tuesday -- was being offered to accommodate people from different time zones and to allow for any technical problems that might result from a last-minute rush of applicants.

The HealthCare.gov site had a disastrous, glitch-prone debut in October but has gone through extensive improvements to make it more reliable and increase its capacity, and the administration said the system was running well Monday.

By the afternoon, the site had received a record 850,000 visits, five times the number logged by the same time last Monday, the administration said. Bataille said the system was handling the volume with error rates of less than 1 in 200 and response times of less than one second.

The Obama administration is hoping for a surge of year-end enrollments to show that the technical problems were merely a temporary setback. That would also go a long way toward easing concerns that insurance companies won't be able to sign up enough young, healthy people to keep prices low for everyone.

But the grace period may have been a tacit acknowledgement that the website remains vulnerable to heavy traffic. What's more, the delay offered critics of "Obamacare" another opportunity to argue that the law still isn't working and that Obama keeps changing the rules.

In Ohio, Lt. Gov. Mary Taylor called the deadline extension "a clear sign Healthcare.gov continues to struggle."

"Consumers are already confused and insurers are overwhelmed with the administration's last-minute changes, yet there seems to be no end in sight," Taylor, a Republican who heads Ohio's insurance department, said.

The administration was careful not to characterize Tuesday as a new deadline or an extension, likening the move instead to the Election Day practice in which people who are in line when the polls close are still allowed to vote.

The government's original deadline already had been pushed back a week because of the website problems. The extra day will add to the already daunting administrative problems that insurance companies face, such as inaccuracies on applications, said industry consultant Robert Laszewski.

"Insurers would like to have two to three weeks to process applications. Now they're going to have a week, less one more day," he said. "When the day is done, it doesn't help."

Obama said on Friday that more than 1 million Americans had enrolled for coverage since Oct. 1. The administration's estimates call for 3.3 million to sign up by Dec. 31, and the target is 7 million by the end of March. After that, people who fail to buy coverage can face tax penalties.

Monday had been the deadline for Americans in the 36 states served by the federal site to sign up if they wanted coverage at the start of the new year. The remaining states operate their own online marketplaces, and some of them have also extended their deadlines.

As the deadline drew near, more than 1 million people visited the website over the weekend, and a federal call centre received more than 200,000 calls.