NEW YORK — With the fate of the health care reform law hanging in the balance, three of the country’s largest health insurers said they would maintain some Affordable Care Act benefits regardless of how the Supreme Court rules on it. But the companies said they would not continue coverage for pre-existing conditions.

With the court expected to rule by July, UnitedHealth Group Inc. and Humana Inc. said customers could keep their children on plans until age 26, get free preventive care such as diabetes screenings and won’t face lifetime benefit limits. They also will not rescind policies except in cases of fraud and will maintain a simplified appeals process for denials.
Aetna Inc. said it would let young adults stay on parents’ plans, cover preventive services and maintain independent reviews of coverage denial ­appeals.

The benefits had been in doubt after the Supreme Court in March heard arguments about the constitutionality of the 2010 health care law, especially the individual mandate requiring most Americans to obtain health insurance.

“The protections we are voluntarily extending are good for people’s health, promote broader access to quality care and contribute to helping control rising health care costs,” said Stephen Hemsley, chief executive officer of UnitedHealth, the nation’s largest health insurer. The company had nearly 26 million people in its commercial plans last year.

“Humana believes its health plan members should have the peace of mind of knowing the company embraces and will maintain these commonsense provisions that add stability and security to health care coverage,” the Louisville, Ky.-based company said in a ­statement.

Hartford, Conn.-based Aetna said in an e-mail, “A number of provisions in the health reform law have been woven into the fabric of our health care system, bring value to customers and consumers, and should be maintained.”

None of the companies discussed coverage of adults with pre-existing conditions. UnitedHealth said one company alone cannot cover children under 19 with pre-existing conditions, so it is “committed to working with other participants in the health care system to sustain that coverage.”

Allowing families to keep children on their plans until age 26 expanded coverage — including pharmacy benefits — to about 2.5 million people in 2011 while increasing premiums less than 1%, the government ­estimates.

The provision is among the most popular parts of the law, surveys show, and the Commonwealth Fund has estimated that some 6.6 million young adults are on parents’ plans. The bottom line, fund president Karen Davis told reporters, is that when affordable coverage is available, young people will enroll. “They don’t think they are immortal.’’
The government has estimated that barring lifetime limits on benefits also adds less than 1% to premiums.

Of the various parts of the law being considered by the court, the individual mandate is considered the most vulnerable. If it is struck down it would undermine new online insurance “exchanges” where some 20 million people, mainly those without employer coverage, are supposed to shop for plans — with federal subsidies for the needy.
Already 14 states, including California, have authorized creation of exchanges where individuals and small businesses could purchase coverage.

If the individual mandate is rejected, 39 million Americans would lack health insurance by 2021, according to the Congressional Budget Office. That would be 16 million more people than if the justices left the statute standing, the CBO says.

Overturning the individual mandate but leaving most of the law intact would mean fewer drug sales for pharmaceutical companies, according to Moody’s Investor Service. A decision essentially striking down the entire law would give drug makers short-term relief but create long-term market uncertainty over the possibility of government cost control, Moody’s said.

Doctors and hospitals have already responded to the two-year-old statute by altering the way they do business. They are preparing for an influx of new customers and incentives that reward greater coordination among caregivers and penalize poor performers.