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, an Expedia or Orbitz.
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 firms will have separate access to their own exchanges.
The approvals announced Thursday are provisional; administration officials said more work remained to be done before they would issue final sign-offs.
The GOP-led states conditionally approved are Idaho, 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.
A fifth Republican-led state, Mississippi, may yet win approval.
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, including New Jersey and Pennsylvania.
The rest of the states are pursuing partnerships with Washington or still mulling their options.
Two states, Arkansas and Delaware, have been approved for partnerships. The state will handle consumer issues and oversee health plans while Washington does the back-office tasks of enrolling consumers.
Originally a Republican idea, exchanges won bipartisan support, only to be abandoned by many in the GOP once they were put in Obama's health-care law.
The basic concept is that setting up a marketplace with clear-cut rules would benefit consumers and encourage insurers to compete, helping keep costs low. Former Massachusetts Gov. Mitt Romney set up an exchange in that state under his 2006 health-care overhaul law.