ORLANDO — As the Supreme Court prepares to rule on the constitutionality of President Obama's health-care overhaul, Mitt Romney laid out an alternative on Tuesday that would make the health-insurance system more like a "consumer market."

Addressing supporters in Orlando, Romney fleshed out a plan he proposed earlier that would apply free-enterprise principles to the nation's health-care system rather than operate it like a "government-managed utility," letting competition drive down prices and increase quality.

He also vowed to divert federal Medicaid dollars and other federal funding to state governments, making them responsible for covering the uninsured. And he promised that his plan would still help cover people with pre-existing conditions, one of the more popular components of Obama's law.

Romney fiercely attacked what he and other Republicans have labeled "Obamacare." The presumptive GOP presidential nominee said that if the Supreme Court does not overturn the law in full, he would work to repeal whatever remains of it on his first day as president by granting a waiver to all 50 states to opt out of the law's restrictions.

When governor of Massachusetts, Romney signed into law a state plan that Obama and others say served as a model for the Affordable Care Act. "Romneycare" requires that all state residents purchase insurance or pay a penalty and has an array of state and federal subsidies for people who are too poor to afford it. Notwithstanding that, Romney has pledged to repeal Obamacare, and says that other states should be free to adopt the Massachusetts model or not.

Romney first laid out a plan to replace the health-care law in a speech in Michigan last spring before he formally launched his campaign. But he avoided detailed discussions of health care during the Republican primaries, partly because the Massachusetts law he championed and signed drew sharp criticism from many conservatives in his party.

Romney said his top priority is to care for the nation's uninsured, but that he would make states responsible for providing that service.

"I believe that states have responsibility to care for people in the way they feel best," Romney said. "It's important for us, in my view, to make sure that every American has access to good health care."

Romney said he wants to make the nation's health-care system more like a consumer market, likening it to the tire, automobile and air-filter markets that he said keep costs down and quality up. To do so, he said, he would allow individuals and small businesses to buy insurance coverage with the same tax advantage that larger businesses enjoy and to purchase insurance across state lines or join organizations to give them bargaining power with insurers.

"We can get health care to act more like a consumer market, and if we do that and we stop making it like a big government-managed utility, we're going to see better prices, lower costs and better care," Romney said. "It's happened everywhere we've applied consumer-market principles. Free enterprise is the way America works. We need to apply that to health care."

Romney also said his plan would help cover people with pre-existing conditions.

"Let's say someone has been continuously insured and they develop a serious condition, and let's say they lose their job or they change jobs, they move and they go to a new place," Romney said. "I don't want them to be denied insurance because they've got some pre-existing condition."

The Obama campaign hit back at Romney's policy view in a statement Tuesday: "This morning, Mitt Romney promised that if he's elected, insurance companies will be able to discriminate against Americans with pre-existing conditions, charge women higher premiums than they charge men for the same coverage, and kick young adults off their parents' plans when they graduate high school or college. ... For too long, American families have faced a choice between going bankrupt to afford the care they need or going without that care at all, and Mitt Romney wants to take us back to that time."