Facing regulatory crackdowns and intensifying criticism from patients and doctors, the nation’s biggest health insurers said on Friday that they would retreat from tactics that have delayed medical care and led at times to denials for necessary treatments.

For years, the widespread practice known as prior authorization has vexed patients who might not have been notified until the day of surgery whether a procedure would be covered by their insurance or if a prescription medicine would be denied for no clear reason.

Insurers often send unintelligible form letters, leaving patients to puzzle out the basis for the denial or what their next steps should be. Patients may delay or even abandon necessary medical care because they may not even be aware that they can appeal the decisions.

Lawmakers, regulators and public outrage have drawn attention to abuses of the system, leading to mounting calls for reforms. Insurers have also been the target of myriad lawsuits, some of which attributed patient deaths to those denials and delays. The murder of Brian Thompson, a UnitedHealthcare executive, last December renewed criticisms of the tactic, unleashing a barrage of complaints that the practice was deployed to avoid covering care.

“Prior authorization is a huge issue for people who are in managed care plans because it is one of the ways plans use to control their costs,” said David A. Lipschutz, co-director for the Center for Medicare Advocacy. He pointed to several studies showing that insurers may have inappropriately denied care, particularly in private Medicare plans.

Various reports from federal regulators and researchers show that the vast majority of appeals are successful.

Insurers have defended the practice as an effort to rein in heath care costs, citing some high-priced medications, procedures and tests that they say are unnecessary.

In making the announcement, executives from the two main insurance trade groups acknowledged that the growing outcry over the process and said that the plans promised to take a series of voluntary steps over the next year and a half.

“We recognize the frustration people often feel about their experience,” said Mike Tuffin, the chief executive of AHIP, an industry trade group in Washington, D.C. By easing the policies, he said, “we expect patients will feel less friction and more peace of mind.”

The insurers said they had agreed to streamline the process to ensure patients and their doctors get a decision about the treatment when the request is made, saying they hope to answer 80 percent of requests in real time by 2027.

Telling patients and their doctors immediately whether a test or treatment is covered “should alleviate a lot of the surprises,” said Kim Keck, the chief executive of the Blue Cross Blue Shield Association, which represents Blue Cross plans in different states.

Not all the delays are caused by the insurers. They estimate that nearly half of the prior authorization requests submitted by hospitals and doctors are via mail, phone or fax. The insurers said they hoped to work with providers to develop ways to use electronic requests that can be answered more quickly.

Other changes include more standardization over what information doctors and patients need to submit to get approval. The insurers have also agreed to protections for patients who change health plans so they can receive previously approved treatments for at least 90 days.

The insurers have also said they will reduce the number of procedures and tests subject to prior authorization. “All plans have been looking at scope in prior authorization for a long time,” Ms. Keck said.

Dozens of insurers have signed on to the new agreement. The companies include Aetna, Cigna, Kaiser Permanente, UnitedHealthcare and Blue Cross plans in nearly every state, and they cover some 260 million Americans. While there will be some variation in different states and among different employers, the changes apply to both employer-based and government plans under Medicare and Medicaid.

Some companies had already begun making these changes, under growing pressure from lawmakers and regulators.

During the Biden administration, Medicare officials had already enacted stricter rules over the process, and the Trump administration has also taken on the issue.

The new head of Medicare, Chris Klomp, has been in discussions with the health plans, and senior Trump officials are expected to hold a news conference on Monday to discuss the steps they are taking. The federal officials are expected to be supportive of these industry changes but will emphasize the need for accountability.

In a statement, Shawn Martin, the chief executive of the American Academy of Family Physicians, offered support for the insurers’ move but cautioned that the proof would be in how the companies behave in the coming months and years. “While this commitment is a step in the right direction, we will ultimately measure its impact by real changes in the day-to-day experiences of patients and the physicians who care for them,” he said.

Others say the voluntary guidelines are not enough. “We believe these, and other consumer protection commitments should be in statute, and not just voluntary,” said Anthony Wright, the executive director of Families USA, a consumer advocacy organization in Washington, D.C., in a statement.

While emphasizing the need to not burden patients, he said that standardizing and streamlining the process would help patients. “We look forward to working with AHIP and policymakers in Washington and the states to recommend reforms that will ensure people can get the care they need when they need it,” he added.