Republican officials in more than a half-dozen states said they opposed expanding Medicaid or had serious doubts about it, even though the federal government would pick up all the costs in the first few years and at least 90 percent of the expenses after that.

While upholding the most hotly debated part of the health care overhaul law — a requirement that most Americans have health insurance or pay a penalty — the Supreme Court said in its ruling on Thursday that states did not have to expand Medicaid as Congress had intended — leaving a huge question mark over the law’s mechanism for providing coverage to 17 million of the poorest people. …

That potential gap will probably lead to ferocious statehouse battles in the coming year, as states weigh whether to accept billions of dollars in federal aid to pay for expanded coverage. The health care industry, sensing the skepticism in some states, is preparing a campaign to persuade state officials to accept the money for coverage of the uninsured.