WASHINGTON — Large health plans that have claimed financial challenges from their participation in health insurance exchanges under the Affordable Care Act are set to seek significant premium increases in about a dozen states where they operate those individual plans.

Others are limiting the number of plans offered if not vacating states altogether.

Plans in some states say they will file for increases next year of 20% or more, but, since proposals face reviews by state regulators, a complete assessment is unlikely until just prior to November 1, the date that the law’s fourth large enrollment window is due to open.

The dilemma is in making coverage available to everyone — regardless of medical history — at the same price and with limited variation based on age, versus higher insurance costs for many healthy individuals.

Average premium requests for 2017 for the most popular type of ACA marketplace plans are 16% higher in the first nine states to make them public, according to an Avalere Health analysis. The 16% average increase is for all silver-tier plans, which cover an average of about 70% of medical claims.

Another challenge is the move by Highmark Inc., a large insurer in three states, to file a lawsuit against the federal government, alleging a deficit of payments.

Humana Inc. has said it wants to continue to sell coverage through the exchanges — if possible. To do so, the company wants rate increases ranging as high as 70% for its individual health plans in Georgia.

“Those proposed rates reflect many changing factors in the market but are primarily driven by changes in expected claims costs that reflect the rising costs of medical services; changes in Humana’s contracts with hospitals, physicians and other health care providers; and increased use of medical services by Humana members,” said a company spokesman.

Federal officials maintain that, because they get a subsidy linked to their income and the cost of insurance in their area, many consumers who purchase coverage through the online exchanges are unlikely to feel the total impact of the premium adjustments.

“Americans will continue to have affordable coverage options in 2017,” assured Kevin Counihan, chief executive officer of HealthCare.gov. “The vast majority of consumers qualify for tax credits that reduce the cost of coverage below the sticker price.”

One factor that appears certain is that a growing number of health insurance customers in mostly rural regions will have a single option to select from next year. The occurrence of only one insurer in a market is expected to pose a challenge for the Obama administration and could fuel the fire by many Republicans to repeal the controversial health care law.