(Read More: States Eye California’s Crack at Obamacare)

“I was really shocked that 64 percent [of uninsured adults] said they haven’t decided if they will purchase insurance by the Jan. 1 deadline,” Adams said. “I was definitely surprised by the high number of people who really have no clue what they’re going to do next year.”

“We don’t want these consumers to miss this key deadline,” she said, adding that new heath-care exchanges under Obamacare will begin accepting applications for insurance in less than four months. “They’re going to potentially go without health care for the entire year.”

In other findings of the survey, more than 60 percent of Americans said they fear Obamacare will lead to increased health-care costs.

(Read More: President Vows Obamacare Will Meet Deadline)

Just 26 percent predicted such costs will go down under the program, according the survey by InsuranceQuotes, which provides an online marketplace for consumers and insurers to seek and provide quotes for insurance coverage. The web site is part of Bankrate Insurance, an online network owned by Bankrate.com.

A total of 61 percent of the uninsured they don’t having insurance because they can’t afford it, the survey found. And a total of 58 percent of all adults—insured or otherwise—didn’t know if they will be eligible for tax credits to offset their purchase of health insurance, even though a married couple with two kids could make up to $94,000 and still qualify.

The survey, which was conducted by Princeton Survey Research Associates International, had an overall margin of error of 3.6 percent. At total of 83 percent of those surveyed currently have health insurance, while 17 percent were uninsured—which tracks that national proportions.

(Read More: Uh Oh, Obamacare Math Sinks In for Small Businesses)

Under the ACA, uninsured Americans have until the beginning of 2014 to purchase insurance through health-care exchanges being set up nationwide or other venues—or face a financial penalty. That penalty is equal to $95 per adult, and $47.50 per child, up to a maximum of $285—or 1 percent of household income, whichever is greater.

Those penalties will escalate in future years.

Adams of InsuranceQuotes.com said uninsured people might be holding off making a decision on buying health insurance because “folks are saying that the penalty is low.”

“But I have a feeling that it’s more that they’re not educated,” she said.

“It’s not surprising that people are confused and uninformed,” Adams said. “It’s a complicated system. It involves a lot of detail that the average person, unfortunately, is not going to grasp.”

That confusion not only could hurt individuals’ wallets—by making them pay out-of-pocket for health care as needed—but also put financial pressure on insurers offering coverage through exchanges set up under the ACA.

That system is predicated on the theory that enough healthy people will enroll and buy insurance so that their premiums will offset the costs of benefits for less healthy people in the same plan. If not enough healthy people sign up, Adams noted, insurers will be on the hook for the benefit payouts regardless, cutting into, or erasing their profits.

“If only the sick enroll,” Adams warned, “it could be very precarious for the industry and the cost of insurance.”

Adams said ignorance could hit lower-income Americans particularly hard.

“There were 68 percent of people who are earning under $30,000, who are not sure what they’re going to do,” Adams said, despite the fact that “they are certainly eligible” for tax credits to offset the costs of buying insurance under the ACA.

“They should” sign up, she said.

Adams noted that if poor adults without dependents live in states that are not expanding their Medicaid programs under Obamacare, they risk not being covered by that health-insurance program despite making the same low wages as adults who have dependents.

More from Dave Mangum at CNBC

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—By CNBC’s Dan Mangan. Follow him on Twitter @danpostman.