Other services that must be offered at no charge include counseling to help people stop smoking; screening and counseling for obesity; and tests for infection with the virus that causes AIDS.

“Getting rid of cost-sharing is a long-overdue step in the right direction,” said Kenneth E. Thorpe, a professor of health policy at Emory University in Atlanta. “But we will have to do a major public education campaign to get people to take advantage of these clinical preventive services.”

The rules stipulate that no co-payments can be charged for tests and screenings recommended by the United States Preventive Services Task Force, an independent panel of scientific experts. The rules apply to new health plans that begin coverage after Sept. 23 and to existing health plans that make significant changes after that date. The administration said the requirements could increase premiums by 1.5 percent, on average.

Kathleen Sebelius, the secretary of health and human services, said the rules would extend benefits to 31 million people in new employer-sponsored plans and 10 million people in new individual plans next year.

In many cases, insurers will be allowed to charge for goods and services needed to treat a condition detected in a screening. For example, consumers can receive free screenings for depression and high cholesterol, but they might be charged co-payments for antidepressants and cholesterol-lowering drugs.