WASHINGTON — The Obama administration said Tuesday that 11.7 million Americans now have private health insurance through federal and state marketplaces, with 86 percent of them receiving financial assistance from the federal government to help pay premiums.

About three-fourths of people with marketplace coverage — 8.8 million consumers — live in the 37 states served by HealthCare.gov, the website for the federal insurance exchange. The other 2.9 million people are in states that created and operate their own exchanges.

Sylvia Mathews Burwell, the secretary of health and human services, underlined the importance of subsidies for people in states using the federal exchange — subsidies that could be withdrawn if the Supreme Court rules against the Obama administration in a pending case.

Administration officials suggested that more than seven million people could lose subsidies, making insurance unaffordable, if the court ruled that such assistance was unavailable in the federal exchange. The plaintiffs contend that the Affordable Care Act does not allow subsidies in the federal exchange.