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In another announcement promoting the Affordable Care Act ahead of a Supreme Court decision on challenges to the law, President Barack Obama's administration said Thursday that 12.8 million Americans will receive rebates on their health insurance premiums at an average of $151 per household.

About 588,000 Missouri residents and 300,000 Illinois residents will be eligible for rebates because their insurance companies overspent on administrative costs, triggering refunds under Obama's health care overhaul that passed in 2010.

The rebates are a fallout of the law's requirement that insurance companies spend at least 80 percent of the premiums they collect on medical care and quality improvement or return the difference to consumers and employers.

Insurance companies providing coverage in Missouri and Illinois owe more than $60 million to policy holders in each state, according to the administration. The rebates are due by Aug. 1.

Analysts have said that the majority of Americans who are insured through their employers will probably not be issued a direct refund. Because employers typically pay a greater share of the premium, they'll get most of the rebate money to go toward reducing employees' health care costs.

According to the administration's report, 2.6 million households due rebates purchased their coverage directly from an insurance company, the group most likely to get a check in the mail.

A report earlier this year from Consumers Union said insurance companies Anthem Blue Cross & Blue Shield, Blue Cross Blue Shield of Kansas City and United Healthcare will owe the most to individual and small-business policy holders in Missouri.

Larger employers that are self-insured are exempt from the rebate requirement.

The decision from the Supreme Court on the law's constitutionality is expected by the end of the month. Most of the challenges stem from the law's requirement that nearly all Americans buy health insurance or pay a fine.

If the entire law is thrown out, health policy analysts expect a chaotic situation because many programs have already launched, including preventive care with no co-pays for Medicare recipients and extended coverage for young adults on their parents' policies.

The administration has been touting the changes in the run-up to the ruling.

On Wednesday, Health and Human Services Secretary Kathleen Sebelius announced grant money to expand health clinics that serve people with government insurance, including about $600,000 for the mental health provider Comtrea of Jefferson County to add primary and dental health to its services.

The Associated Press contributed to this report.