Alliestean Reese, left, works with Cecila Edwards, with her Affordable Care Act application at a Miami Health Fair on March 15. Despite Florida Republicans' efforts to fight the Affordable Care Act at every turn, more than 440,000 Florida residents had been enrolled through the federal marketplace through the end of February.

WASHINGTON - Millions of Americans could get extra time to enroll for taxpayer-subsidized coverage this year under President Barack Obama's health care law, allowing the administration to boost sign-ups and the political fortunes of Democrats under attack over the program's troubles.

The Health and Human Services Department Wednesday posted two documents that detail "special enrollment periods" for broad groups of people trying to access new online health insurance markets.

Those who've started an application, but weren't able to finish before the March 31 open enrollment deadline, will get a limited amount of time to sign up for coverage that would take effect May 1.

Additionally, people in 10 general categories of special circumstances would also get additional time to apply -- up to 60 days. The categories include exceptional circumstances such as natural disasters, system errors related to immigration status, computer error messages due to technical difficulties and situations involving domestic abuse, as well as other sorts of problems.

Explaining the extra time, the administration said it anticipates that heavy interest between now and Monday "could potentially keep consumers from completing the enrollment process despite their efforts to meet the deadline."

Special enrollment periods are allowed under the law, but previously they were mainly expected to be used to accommodate changes in life circumstances, such as marriage, divorce, the birth of a child or job loss.

The latest tweaks to health overhaul rules drew immediate scorn from Republicans committed to repealing "Obamacare."

"The administration has now handed out so many waivers, special favors and exemptions to help Democrats out politically ... it's basically become the legal equivalent of Swiss cheese," Senate Minority Leader Mitch McConnell, R-Ky., said Wednesday.

The late-innings announcement added to a perception of disarray that has dogged the health care overhaul from its early days. It also raised concerns about the potential for another round of technology problems such as the ones that paralyzed HealthCare.gov after its Oct. 1 launch.

There seemed to be three major factors involved:

-- Concern about turning away thousands of people who may belatedly try to enroll this week. A recent Kaiser Family Foundation poll found that 6 in 10 uninsured people were unaware of the March 31 enrollment deadline, and half said they didn't plan to get coverage. It can take several visits to the website to finish an application.

-- Many consumers trying to use the new markets may still be getting tangled up in the complicated enrollment process. The administration's own numbers show that only about half of the people deemed eligible to enroll through March 1 actually went all the way through to signing up. More than 4 million people either abandoned their applications or may still be trying to muddle through.

-- Obama himself has been leading a last-minute drive to entice Hispanics to sign up. The nation's largest minority -- with the highest uninsured rate of any race or ethnic group -- has been on the sidelines and risks being left behind in the drive to expand coverage.

The White House is scrambling to meet a goal of 6 million signed up through new online markets that offer subsidized private health insurance to people without access to coverage on the job.

"We are experiencing a surge in demand and are making sure that we will be ready to help consumers who may be in line by the deadline to complete enrollment, either online or over the phone," said HHS spokesman Aaron Albright.

Officials say the federal website is holding up well under the added demand, with more than 1.2 million visits on Tuesday. But independent testing by Detroit-based Compuware has found that the site runs slowly when compared to other health insurance industry websites.

Officials said the grace period for people in line by March 31 will be available on the honor system.

How long the extension will last depends on individual circumstances. HHS said it will process paper applications received by April 7. Those applying online may have more time, until April 15, the same as the tax filing deadline. People who are due tax refunds may be willing to put some of that money toward health care premiums.

The sign-up extension and the announcement of special enrollment periods follow other delays, most significantly of the law's requirements that medium- to large-sized businesses provide coverage or face fines.

Republicans are making repeal of the health care law their rallying cry in the fall congressional elections. If the various extensions succeed in boosting enrollment, that would help Democratic candidates, including politically vulnerable senators who voted for the law's passage in 2010. Democrats are campaigning to fix the law's problems, not repeal.

The White House had signaled last week that a grace period of some sort was in the works. Spokesman Jay Carney said Friday that people in line by the deadline would be able to complete their applications. Administration officials argue that's not extending the deadline. They compare it to the Election Day practice of allowing people to vote if they are in line when the polls close.

The administration's actions primarily affect the 36 states where the federal government is taking the lead on sign-ups. But the 14 states running their own websites are likely to follow, since some had been pressing for an extension on account of their own technical problems.

Brian Haile, senior vice president for health policy at the Jackson Hewitt tax preparation firm, welcomed the move.

"The disbursement of tax refunds appears to be making a substantial difference in the willingness and ability of uninsured Americans to sign up for ... coverage," Haile said.