WASHINGTON — With open enrollment for millions of uninsured Americans just nine months away — Oct. 1 — the four Republican-led states became part of a group totaling 17 states plus Washington, D.C., that received an initial go-ahead to build and run insurance exchanges. Seven were approved Thursday.

Significantly, the list also included California, which has nearly 7.5 million uninsured residents, more than any other state. Democratic-led California was an early supporter of President Barack Obama’s health care law and had been working diligently on its plan.

The approvals announced Thursday are provisional; administration officials said more work remains to be done before they’ll issue final sign-offs.

In addition to Idaho, the GOP-led states conditionally approved are Nevada, New Mexico and Utah. Idaho and Utah have Republican governors and legislatures. Nevada and New Mexico have GOP governors, but Democrats control their legislatures.

“We’re on track for Idaho having a say over how this process works, instead of having the federal government dictate all of it,” said Jon Hanian, spokesman for Republican Gov. Butch Otter. The Legislature still has to weigh in.

Insurance exchanges are not something consumers are familiar with.

“Most people don’t really know what those words mean, but that’s OK,” said Rachel Klein, executive director of Enroll America, a nonprofit trying to educate the public about new benefits under the federal health care law. “What they really need to know is that there’s going to be a new way to buy health insurance.”

The new marketplaces are supposed to take the confusion and anxiety out of buying private health insurance for individuals and families who buy their coverage directly.

Exchanges are meant to have the feel of an online travel site, like Expedia or Orbitz, for example.

Exchanges will also offer some relief from sticker shock. Under the new law, about 8 in 10 customers in the new marketplaces will be eligible for income-based federal aid to help pay their premiums.

Small businesses will have separate access to their own exchanges.

The federal government will set up and run the new marketplaces in states that opt out of playing any role, and 19 Republican-led states have taken that route.

The rest of the states are either pursuing partnerships with Washington or still mulling their options.

Two states, Arkansas and Delaware, have been approved for partnerships. That means a state will handle consumer issues and oversee health plans while Washington takes on the back-office tasks of enrolling consumers and determining subsidies.

Right now, exchanges exist in only a couple of states, although some large private employers are also experimenting with them.

Under Obama’s law, plans in the new marketplaces will have to cover a set of “essential” benefits, including hospitalization, doctor visits, prescriptions, prevention and care for pregnant women and young children. Costs to the consumer will be the main difference among plans, with four levels of coverage: bronze, silver, gold and platinum. A consumer with a bronze plan will pay lower monthly premiums, but would face higher cost-sharing for medical care.

Exchanges will also steer people with low incomes to state Medicaid programs. The law gives states the option to expand Medicaid to cover more of their low income residents, with the federal government picking up about 90 cents of every dollar in added costs.

Coverage through exchange plans will begin on Jan. 1, 2014.

The law will require most Americans to carry health insurance, either through an employer, a government program or by buying their own policies.

Insurance companies may not turn away the sick or charge them more. There also will be limits on what insurers can charge older customers.