Monday marks the last day to sign up through the federal and state health exchanges to have insurance coverage beginning Jan. 1. And while government officials said the federal site, HealthCare.gov, can handle a last-minute rush of consumers, there's still fear that the word may not be getting out to the people who most need to enroll.

"It's certainly important to people who are used to having some coverage because they want to make sure there's no gap in coverage," said Ron Pollack, executive director of Families USA, a non-profit care advocacy group. The biggest concern, he said, is people who "had coverage, but it may have been inadequate or unaffordable, or they may have been in high risk pools—for those groups, getting enrolled by Dec. 23 is absolutely a priority."

People may enroll on the marketplaces until March 31 to gain insurance and avoid having to pay a fee for not having , as is now required by the law. But Pollack said it is particularly important for some groups of people to sign up now to have coverage in January:

—Those whose pre-existing condition insurance plans will end Dec. 31.

—Those who lost coverage when insurers canceled 2013 plans that did not meet the required standards of the Affordable Care Act.

—People in states where Medicaid is scaling back.

"There's been a special outreach to the people in the high-risk pools and who received termination notices," Pollack said. "For those who have not had coverage in the past, but haven't needed coverage, they may not feel quite the same sense of urgency."

Julie Bataille, director of the office of communications for the Centers for Medicare and Medicaid Services, said the government expects to be able to handle the volume created by the deadline. Healthcare.gov can now handle at least 800,000 people a day, and if the system begins to run slowly, Bataille said a queuing system will allow people to leave their e-mail addresses. When the site becomes available, they get an e-mail that lets them be placed at the front of the line when they return.

The government has also added 800 new people to the call centers, so more than 12,000 people are available to answer questions. Workers also received training to address questions specific to the deadline. About 80,000 navigators and certified application agents have been trained across the country to answer questions one-on-one.

In some areas, the word is still taking a while to get out. Some insurers held back on advertising until the website was fixed, and some state governments have continued an anti-Affordable Care Act stance by not promoting the exchanges at all.

In Ohio, for example, the state's online health page offers no explanations of the law, only links to the federal exchange and the required regulatory information.

"They've taken a position that we don't have to do anything about this,'" said Kathleen Gmeiner, project director for Ohio Consumers for Health Coverage. "The insurance commissioner has made it very clear over the past two years that she opposes the ACA and she opposes the marketplace."

But proponents of the law say slow advertising efforts, following the flawed Oct. 1 launch of HealthCare.gov, have also contributed to consumers not knowing their options. President Obama announced Friday that more than a million people had signed up for both the state and federal exchanges, most of them in December. When Healthcare.gov launched, consumers faced frozen pages, lost applications and long wait times. Those issues have been fixed and the site is running properly, Bataille said.

In addition to technical problems, repeated efforts by Republicans to repeal the law may have confused consumers about the need to sign up.

"It's so amazing that so many people still think the law was either repealed or never got passed," Gmeiner said. "One senior said, 'You're talking as if this is really going to happen.' Well, it's happening. But we've got a big row to hoe when it comes to getting the word out."

In New Mexico, the state had not been aggressive in marketing the health care exchange because of the botched federal roll-out. But it is now stepping up its efforts.

"We've changed a lot of our marketing," said Debra Hammer, spokeswoman for the New Mexico Health Insurance Exchange. "We held back on it because we knew there was some frustration with the federal website."

In one week in December, the state gained 1,000 new "likes" for a Facebook page, which has now received more than 7,000 "likes", and more than 29,000 people have viewed a video for the state's large Native-American community, she said.

"We know that insurance is really complicated," she said. "We're trying to use the social media to educate people. What's a pre-existing condition? What' s a deductible?"

Navigators, or those who can assist people through the process, are "booked out," she said, so the state is looking at hiring more, and conducting group enrollment sessions. Several states, cities and community organizations have started "enrollment fairs," where people can sign up in groups with guided help.

Robert Zirkelbach, spokesman for America's Health Insurance Plans, said insurers are working to educate people about their options, as well as to help them enroll.

"Our industry wants to make sure people don't experience gaps in their coverage due to issues outside their control," he said, citing the website problems and canceled plans.

But he said there has been some confusion: People will not gain coverage until they pay their first month's premium, which is done through the insurer, not through HealthCare.gov. Because of the confusion, people have until Jan. 10 to pay their premium, he said. So people who register by Monday and pay their premium by Jan. 10 will have coverage retroactive to Jan. 1.