Each state exchange will certify “qualified health plans,” provide the public with “standardized comparative information” on costs and benefits, and rate each plan based on the quality and price of care. In addition, the exchange will help people determine if they are eligible for Medicaid or the Children’s Health Insurance Program, or for federal tax credits to subsidize the purchase of private insurance.

Federal officials said they would issue a separate rule later this year specifying the “essential health benefits” that must be offered by all health plans.

Trumpeting the advent of the exchanges, the administration said Monday that they would “give Americans the same insurance choices as members of Congress.” However, in response to questions after a news conference on Monday, health officials acknowledged that this claim was not necessarily correct.

A small employer will be able to pick “a level of coverage” for its employees. A higher level will pay more of the consumer’s medical costs. Under the law, members of Congress must generally get their coverage through an exchange. But a small business could legally choose a level of coverage lower than those offered to federal employees, including members of Congress.

Under the rules, an employer may allow employees to choose any health plan at a given level of coverage. But an exchange may also allow an employer to limit its workers to one or two health plans — far fewer than the number available to members of Congress and other federal workers.

With some states like Florida balking at the new law, federal officials went out of their way Monday to strike a conciliatory note, promising to be flexible. If a state is not ready by January 2013, Ms. Sebelius said, it still might qualify for “conditional approval” if it was on track to operate an exchange by January 2014. In addition, federal officials said, a state could set up and operate its own exchange in 2015 or later years if it is not ready in 2104.