WASHINGTON – As speculation over the fate of the federal health care law heightens in anticipation of the Supreme Court ruling, at least three major insurers promised Monday to continue following some of the rules in the law that already are in effect.

United Healthcare, which covers about 26 million people in plans that could be affected by the regulations, was the first to make the move.

The company said it would allow young adults to stay on their parents’ policies up to age 26, wouldn’t reinstate lifetime limits on coverage and would continue to offer cancer screenings and other preventive services without co-payments. It also would maintain a third-party appeals process for treatment denials and wouldn’t cancel policies retroactively.

Later Monday, Humana said it would continue those same provisions.

Aetna, too, said it would retain the young adult provision, the preventive care benefits and a third-party appeals program. Aetna’s announcement didn’t include a reference to lifetime limits on coverage or retroactive cancellation.

These consumer provisions score high on public opinion polls, even among people who say they don’t like the overall law. None of the insurers made any comment about other significant provisions in the law, such as the requirement that in 2014 they stop rejecting applicants with pre-existing medical conditions.

Policy experts widely saw the announcements as good public relations moves by the insurers, which probably are hearing from consumers worried that a court decision could mean that their adult children wouldn’t remain on their policies or they might lose access to preventive services.

“They’re trying to hedge against the possibility that some or all of the law will be overturned and they want to be viewed as doing the right thing,” said Chas Roades, chief research officer at the Advisory Board Co., a research firm in Washington.

And they may have been influenced by comments from some congressional Republicans who want to keep some of those rules, even if the law itself is rejected, said Robert Laszewski of Health Policy and Strategy Associates, a consulting firm in Alexandria, Va.

“If the Republicans are going to make you do it, why not do it yourself and take credit for it? It’s smart politics and policy,” said Laszewski, a former industry executive.

Still, some insurers said they didn’t want to make any promises before the decision.

“We are hoping the Affordable Care Act will be upheld,” said Stephen Shivinsky of Blue Shield of California. “We don’t want to say anything before the decision that would make it easier for the court to rule against the law.”

The Supreme Court justices are expected to issue their decision on whether the health law is constitutional sometime this month. They might uphold it, remove parts of it or reject the entire law.

The outcome that insurers fear most would be for the court to strip the law of its requirement that nearly all Americans buy coverage, but to leave in place other rules that govern the industry, including the measure that insurers must accept all applicants starting in 2014.