WASHINGTON — More than 85 percent of Americans who signed up for health coverage this year through the Affordable Care Act qualified for government subsidies, according to a new report that underscores the scope of the aid at a time when the Supreme Court is considering sharply restricting it.

Altogether, close to 10 million of the 11.7 million people who enrolled in coverage this year could get subsidies, the report from the U.S. Department of Health and Human Services shows. Of that, nearly 1.3 million Californians qualified for assistance.

Reliance on government aid is higher in states where the federal government operates insurance marketplaces than in states like California that run their own systems.

The legal challenge being considered by the Supreme Court would strip away subsidies in states that rely on the federal government, affecting as many as 7.7 million people, according to the report.

In many of those states, consumers are getting subsidies that top $300 a month on average, according to the data.

In Mississippi, for example, that has meant the difference between an average monthly premium of $405 without subsidies and $52 with them. In Texas, the average premium drops from $328 a month to $89 a month with aid.

“We now know in very tangible terms how much assistance the Affordable Care Act is providing to people,” said Larry Levitt, senior vice president at the nonprofit Kaiser Family Foundation, which has been closely tracking implementation of the law.

“These subsidies have put health insurance within reach for people who couldn’t possibly pay hundreds of dollars per month on their own.”

The 2010 health law allows Americans who don’t get health benefits at work to shop among plans on state-based marketplaces. The marketplaces are operated by the federal government in 37 states and by the states themselves in the rest, including California, Connecticut and Maryland.