WASHINGTON — Older members of Congress and those who smoke, like Speaker John A. Boehner, could be facing much higher health insurance premiums under a new official interpretation of President Obama’s health care law.

The administration said Wednesday that the government would continue contributing to the cost of health benefits for lawmakers and thousands of Congressional employees, but that they would have to buy coverage as individuals through new state-based markets known as insurance exchanges.

Federal workers, including lawmakers, now generally get coverage through the Federal Employees Health Benefits Program, the nation’s largest employer-sponsored health insurance program. Under some of the most popular health plans, the government contributes $5,000 a year for individual coverage and $11,000 for family coverage.

The 2010 health care law generally requires members of Congress and employees in their “official offices” to get coverage through the exchanges. The purpose was to make sure lawmakers understood the benefits and burdens of the law, as experienced by many of their constituents.