Medicaid is about to take a starring role in the national health care debate.

Today, only certain people qualify for the health insurance program for the very poor: the elderly, the disabled, pregnant women and children. Under its proposed expansion, any poor American could qualify — a key part of health care reform.

But thanks to the recent U.S. Supreme Court ruling, decisions about expanding Medicaid have been left to the states. And Gov. Rick Scott was the first governor in the land to declare he wouldn’t do it.

“There’s no way that Floridians can pay for that,” he told Fox News host Greta Van Susteren, a day after the law was upheld. “This is an expansion that doesn’t make any sense.”

Scott’s main point is that the state’s annual Medicaid expenses already have ballooned to $20 billion — nearly a third of the entire state budget.

But to others — especially health policy experts and the hospitals that treat the uninsured in their emergency rooms — an expansion makes sense.

Consider:

• By most measures, Florida has a thrifty Medicaid program, with a per-person spending rate far below the national average.

• Medicaid spending has gone up primarily because more people have signed up for the program since the beginning of the Great Recession.

• The expansion under the reform law would bring millions in federal dollars to help people who are now uninsured. The federal government foots the entire bill for expanded coverage during the first three years, and 90 percent or more of it until 2020.

In fact, health experts warn that not expanding Medicaid could cost Floridians, because many of the state’s 3.8 million uninsured residents will continue to receive care they can’t pay for in hospital ERs. Those costs ultimately are passed down in the form of higher insurance premiums for everyone else.

“We have an opportunity here,” said Anthony Carvalho, president of the Safety Net Hospital Alliance of Florida, which represents hospitals such as Tampa General, which care for the poorest and sickest patients. “It’s a very significant opportunity to bring health coverage, health access to Floridians that don’t have it.”

Established in 1965, Medicaid is a program jointly run by federal and state governments that provides free or low-cost health coverage to poor families, children, pregnant women, elderly people and the disabled.

More than 3 million Floridians are enrolled in one of several Medicaid programs. About 70 percent of Medicaid services provide acute care, which includes hospital stays, outpatient procedures and doctor visits. The remaining 30 percent goes to long-term care such as nursing homes and home health services.

Currently, the federal government foots 55 percent of the total Medicaid bill in Florida.

But the state’s tab has grown steadily, from about $14.8 billion in 2007 to $20.3 billion this past year, a 37 percent increase.

The growth, however, has been driven largely by enrollment, not rising costs. Enrollment has increased more than 50 percent over the same period, from 2.1 million to about 3.2 million.

“You can’t argue that because you’re covering more people, that somehow it’s out of control,” said Bruce Rueben, president of the Florida Hospital Association, which supports the Medicaid expansion.