Continued from page 1

Only about 5 percent of the city’s population is uninsured, because of aggressive efforts to cover residents under Medicaid or the D.C. Healthcare Alliance, which enrolls many immigrants who are not eligible for the federal insurance program, officials said.

In Maryland, leaders have wholeheartedly embraced the health care law since its passage. The heavily Democratic state is one of 14 states that have established exchanges through the legislature or by an executive order.

“Today’s decision gives considerable momentum to our health care reform efforts here in Maryland,” said Mr. O’Malley and Mr. Brown, both Democrats.

The General Assembly passed bills in 2011 and this year that set the framework for a health benefits exchange, which state officials say could provide health care access to as many as half of the state’s 700,000 uninsured residents.

By diving into health care reform, the state has already received $34.4 million in federal grants toward getting the exchange up and running and has allotted $26.5 million in the upcoming fiscal 2013 budget to support its implementation.