The administration’s decision was another setback for the new law, which is under attack in court, in Congress and in many state legislatures. Ms. Sebelius said her decision “does not affect the rest of the health care law,” which is supposed to provide coverage to more than 30 million people who are uninsured.

But the Senate Republican leader, Mitch McConnell of Kentucky, said the long-term care program was “only one of the unwise, unsustainable components of an unwise, unsustainable law.” He and other Republicans in Congress want to repeal the entire law.

Advocates for older Americans and people with disabilities expressed disappointment at the decision, and Ms. Sebelius said Americans still had an “enormous need” for long-term care insurance. “At $75,000 a year for a nursing home and $18,000 a year for home health care, most families cannot afford to pay out of pocket,” she said.

The program was intended for people with severe disabilities who wanted to live in the community, though benefits could also have been used to help pay for nursing home care or assisted living. It would have been financed with premiums paid by workers, through voluntary payroll deductions, with no federal subsidy. Premiums were supposed to have ensured the solvency of the program over 75 years.

But Ms. Sebelius said she agreed with actuaries who feared that “not enough young, healthy people” would enroll. “This could have led to a vicious cycle where premiums would have to be set higher and higher to cover the likely costs of benefits, leading fewer and fewer healthier people to sign up for the program,” Ms. Sebelius said.