WASHINGTON — Obama administration officials, urging people to sign up for health insurance under the Affordable Care Act, have trumpeted the low premiums available on the law’s new marketplaces.

But for many consumers, the sticker shock is coming not on the front end, when they purchase the plans, but on the back end when they get sick: sky-high deductibles that are leaving some newly insured feeling nearly as vulnerable as they were before they had coverage.

“The deductible, $3,000 a year, makes it impossible to actually go to the doctor,” said David R. Reines, 60, of Jefferson Township, N.J., a former hardware salesman with chronic knee pain. “We have insurance, but can’t afford to use it.”

In many states, more than half the plans offered for sale through HealthCare.gov, the federal online marketplace, have a deductible of $3,000 or more, a New York Times review has found. Those deductibles are causing concern among Democrats — and some Republican detractors of the health law, who once pushed high-deductible health plans in the belief that consumers would be more cost-conscious if they had more of a financial stake or skin in the game.