Insurers in each state will generally be required to provide all benefits required by state laws adopted before Dec. 31, 2011. States can require additional benefits, but will have to pay the extra costs themselves.

Carl E. Schmid, deputy executive director of the AIDS Institute, an advocacy group, said he had hoped the federal government would set explicit, uniform national standards.

“We are disappointed,” Mr. Schmid said. “We thought the federal government would spell out essential health benefits in more detail. Patients respond differently to different drugs and often need multiple drugs at the same time. Under this rule, patients might have access to a total of 500 drugs in one state and more than 1,000 in another state.”

Access to autism treatment may also differ. Stuart Spielman, senior policy adviser at Autism Speaks, an advocacy group, said that 32 states had laws requiring coverage of autism treatments and that other states were considering legislation to impose such requirements.

The rule limits the costs to consumers in several ways. For health plans offered in the small-group market, the deductible amount, paid by consumers before insurance kicks in, generally cannot exceed $2,000 for individual coverage and $4,000 for family coverage. Total out-of-pocket costs will also be subject to limits. If a health plan has a network of doctors and hospitals, consumers may be required to pay more if they go outside the network.

The new rule generally applies to all health insurers offering coverage in the individual and small group markets. States will have primary responsibility for enforcing the standards. The federal government said it would step in if it found that a state was not doing an adequate job of protecting consumers.

Federal officials acknowledged that many policies sold in the individual insurance market did not cover all the services required in the new rule. The administration said that many small business health plans “meet or are close to meeting the coverage requirements.”

Under the rule, health plans must provide benefits that have not always been provided by commercial insurers. For example, insurers must cover dental care and vision services for children, as well as “habilitative services” to help people with disabilities keep or improve their skills.