Paul B. Ginsburg, the president of the nonpartisan Center for Studying Health System Change, said: “The individual insurance market is now up for grabs. Blue Cross plans will face a lot more competition. Many products sold in the insurance exchanges will have more limited networks of doctors and hospitals than has been the norm in employer-based coverage.”

Moreover, Mr. Ginsburg said: “Consumers will receive federal subsidies based on their income, not on the plans they choose. That creates a strong incentive for consumers to seek plans with lower premiums.”

Federal officials said that consumers shopping for private insurance in the exchanges would often benefit from the same type of competition Medicare patients see when choosing prescription drug plans. Many industry experts doubted that stand-alone drug coverage could succeed, but Medicare beneficiaries now have a choice of more than 20 drug plans in every state, and the average premiums have been relatively stable in the last few years.

May 3 was the deadline for insurers to file applications to participate in markets run by the federal government, but administration officials said they were still trying to expand the options available in states where they wanted more competition.

The upbeat assessment by federal officials follows months of criticism by Republicans and some Democrats who said the administration had fumbled the rollout of the new health care law. Senator Mitch McConnell of Kentucky, the Republican leader, predicted recently that the law would be “the biggest issue” in Congressional elections next year.

In at least 31 states, administration officials said, consumers will be able to sign up for a new kind of product offered by private insurers under contract with the federal Office of Personnel Management, the agency that arranges health benefits for federal employees.

These multistate plans will be available in all states by 2017. They were included in the health care law as a substitute for a pure government-run insurance program — the “public option” sought by liberal Democrats and reviled by Republicans.