WASHINGTON — Sean Jackson, like tens of thousands of other Americans, has had trouble signing up for medical coverage using the HealthCare.gov insurance marketplace, despite several attempts.

“I was able to create an account on Oct. 2, and I haven’t been able to get into there since,” said Jackson, a sports journalist living in Ohio, a note of annoyance in his voice. “I’ll try at random times, like late at night or early in the morning. I sign in. It just goes to a blank screen.”

The economists and policy wonks behind the Affordable Care Act worry that the technical problems bedeviling the federal portal could become much more than an inconvenience. If applicants like Jackson decide to put off or give up on buying coverage, rising prices and even a destabilized insurance market could result.

The enrollment of people like Jackson, who is 32, is vital for the health care law to work. Younger people, who tend to have low anticipated medical costs, are supposed to help pay for the medical costs of older or sicker enrollees. Without them, so-called risk pools in Ohio and other states might become too risky, forcing insurers to raise premiums. Those higher premiums could dissuade more of the young and healthy from signing up, forcing insurers to raise prices again.

Economists warn that in its worst iteration it could lead to a “death spiral” of falling enrollment and climbing prices. They and health analysts said the chances of such a spiral were slim in most states because Americans who go without insurance would face penalties, starting next year. But they said that the problems with the website posed a serious question about the enrollment balance in many state plans.

“If there are significantly more of the older and higher-cost people purchasing coverage than are expected, that’s going to have a significant impact on premiums for the following year,” said Robert Zirkelbach, a spokesman for America’s Health Insurance Plans, a lobbying group.

But getting “young invincibles,” as insurers sometimes call them, to sign up for insurance is an uphill climb. Only about 1 in 4 19- to 29-year-olds is even aware of the exchanges where they might buy affordable insurance, according to a survey this year by the Commonwealth Fund, a nonprofit research group.

The Obama administration has promised to fix the problems with HealthCare.gov by Nov. 30. Insurers would have a good sense of any problems because of under-enrollment by next spring, they said.

Now Democrats, too, talk of delay

Lawmakers from both major political parties on Sunday expressed concern over the botched rollout of the new federal health insurance website, with two Senate Democrats saying the problems are serious enough to justify delays to key provisions of the president’s health-care law.

Republicans, meanwhile, said that the issues were symptomatic of larger problems with the law and that many of the disadvantages of the program are becoming glaringly apparent now that people are starting to be able to see the quality and cost of the coverage available under the law.

Sens. Joe Manchin, D-W.Va., and Jeanne Shaheen, D-N.H., took to the Sunday talk shows to press for legislation they said would give people more time to comply with a rule requiring most Americans to carry health insurance starting next year or face a fine.

Manchin advocated for a bill delaying the so-called “individual mandate” for a year. Shaheen proposed extending the open enrollment period beyond its current end date of March 31 to account for all the people who have not been able to buy coverage thus far because of problems with the online shopping site.

Sebelius to face tough questioning

Republicans said Sunday they intend to press Health and Human Services Secretary Kathleen Sebelius on the Obama administration’s troubled launch of healthcare.gov, the online portal to buy insurance, and concerns about the privacy of information that applicants submit under the new system.

Medicare chief Marilyn Tavenner is to testify during a House hearing Tuesday, followed Wednesday by Sebelius, before the House Energy and Commerce Committee. The officials will also be grilled on how such crippling technical problems could have gone undetected prior to the website’s Oct. 1 launch.

— From wire reports