In the face of growing opposition from hospital and doctors groups, UnitedHealthcare said on Thursday it would delay a plan to stop paying for emergency room visits that it deemed nonurgent, at least until the pandemic has ended.

The policy, which would affect millions of United’s customers, was greeted with longstanding worry over the unintended consequences of the coronavirus crisis on Americans’ health as people put off care for serious illnesses. The change had also sparked outrage in light of the steep declines in E.R. visits that ironically resulted in healthy profits and savings for insurers.

Critics of United’s policy shift said it would exacerbate what experts said was a disconcerting pattern of people shunning emergency rooms in the last year or so, potentially contributing to heart attacks and other illnesses among those who not only feared contagion but also medical bills due to the economic fallout of layoffs and unemployment.

Under the new policy, which was to go into effect next month, UnitedHealthcare, the giant insurer, had planned to scrutinize the medical records of its customers’ visits to emergency departments to determine if it should cover those hospital bills. But in the last week, several major hospital and doctors groups demanded that United abandon the policy.

The decision to hold off “offers a temporary reprieve for patients, and we urge its full and permanent reversal,” Rick Pollack, the chief executive of the American Hospital Association, a trade group, said in a statement. Mr. Pollack had described the policy earlier as “very misguided,” particularly during the pandemic.

In a letter to UnitedHealthcare’s chief executive, Mr. Pollack had sought a policy reversal and emphasized the risks of people not seeking care. “Deferred and delayed care during the pandemic has already contributed to adverse health conditions and increased acuity,” he wrote.

On Thursday, United acknowledged the concerns raised by many groups, in announcing its decision to delay the new policy: “Based on feedback from our provider partners and discussions with medical societies, we have decided to delay the implementation of our emergency department policy until at least the end of the national public health emergency period,” it said in a statement.

Top U.S. health officials have not said what would lead them to declare an end to the crisis.

Hospitals and doctors had raised concerns that the new policy signaled a return to a contentious tactic used by health insurers to clamp down on care they argue should be delivered in a less costly setting.

Anthem, another large insurer that operates for-profit Blue Cross plans, announced a similar policy several years ago that led to a political backlash and a federal lawsuit from emergency room physicians claiming it violated federal protections for patients seeking emergency care. Anthem said it could not comment because of the continuing litigation.

In addition to its questionable timing, the policy shift seemed puzzling since there had already been significant declines in emergency room visits throughout the pandemic into this year. Emergency room visits across the country fell by 27 percent in 2020, compared with the previous year, according to Gist Healthcare, a consultant. which also predicted that people with less serious conditions would continue to stay away.

United’s decision seemed aimed at making sure people did not go back to using the emergency room for nonurgent care, even as hospitals might try to encourage more people to return, said Chas Roades, a co-founder of Gist. Given the potential blowback, he did not believe United was likely to generate significant savings from the program. “I can’t quite believe the juice is really worth the squeeze on this policy right now,” he said.

Physician groups were also critical of the decision to deny coverage for emergency visits that United considered nonurgent. “We object to UnitedHealthcare’s pending policy that asks patients to second guess their instincts that emergency care is needed,” Dr. Susan R. Bailey, the president of the American Medical Association, said in a statement. “Patients should not be expected to self-diagnose to determine whether, for example, chest pain is a heart attack or indigestion.”

Others noted that such a policy could thwart federal efforts to enlist emergency rooms in reaching more people for immunization against the coronavirus.

“This new policy will leave millions fearful of seeking medical care, just as we’re getting hold of the Covid-19 pandemic and trying to get as many people vaccinated as possible,” Dr. Mark Rosenberg, the president of the American College of Emergency Physicians, said in a statement earlier this week.

If United still goes ahead with the change later on, the policy would apply to millions of people in United’s fully insured plans in 35 states, including New York, Ohio, Texas and Washington. People covered through an employer that is self-insured or enrolled in a Medicare Advantage plan or Medicaid would not be affected. The policy would exempt care for children under 2 years old.

United had insisted that its policy was not aimed at preventing customers from going to the emergency room to rule out a heart attack if they had chest pain or to address a medical crisis. The insurer said it would take into account the original reason for the visit, any laboratory work or imaging performed and whether there were existing medical conditions or other factors that could have warranted a visit. A hospital could still attest to the emergency needs, and patients could ultimately appeal.

“Unnecessary use of the emergency room costs nearly $ 32 billion annually, driving up health care costs for everyone,” the company said in a statement on Monday. “We are taking steps to make care more affordable, encouraging people who do not have a health care emergency to seek treatment in a more appropriate setting, such as an urgent care center. If one of our members does receive care in an emergency room for a t issue, like pink eye, we will reimburse the emergency facility according to the member’s benefit plan.”

During the pandemic and for months of lockdown, non-Covid care, ranging from knee surgeries to mammograms to emergency room visits, fell. While some experts worried that the lack of care would cause patients’ conditions to worsen, others argued the drop off might provide evidence that some care, like screenings, was unnecessary.

United’s initial decision was viewed by some critics as a message directed at hospitals.

“They see this as a way to get the upper hand in their perpetual battle with providers,” said Jonathan Kolstad, a health economist at the University of California, Berkeley.

It was the latest example of the insurer clashing with doctors and hospitals, said Michael R. Turpin, a former United executive who is now an executive vice president at USI, an insurance brokerage that helps businesses find coverage. Most recently, United’s sparring with anesthesiologists resulted in lawsuits from a sizable physician-owned practice backed by private-equity investors, and the hospitals complain that United has adopted other policies that make it difficult for patients to get their care covered.

A few consumers are already battling insurers and some providers over billing for Covid vaccines, prompting the federal government to remind the participants that it is illegal to bill patients for those costs.

There is also increasing evidence that some of the people who didn’t go to emergency rooms during the pandemic would have been better off seeking care. Experts pointed to the increase in death rates from heart disease, diabetes and other illnesses that could indicate people were putting off necessary care. A recent study in Health Affairs by researchers from the M.I.T. Sloan School of Management, working with Boston Emergency Medical Services, found evidence of an increase in heart attacks that had occurred out of the hospital, particularly in low-income neighborhoods.

Mr. Pollack noted that even post-pandemic, such a policy would be problematic: “There is no justification for these restrictions now or after the public health emergency,” he said.

The people delaying care may be among those populations that are already the most vulnerable, according to a study by researchers from the Centers for Disease Control and Prevention, which looked at individuals who said they had put off care. “Avoidance of urgent or emergency care was more prevalent among unpaid caregivers for adults, persons with underlying medical conditions, Black adults, Hispanic adults, young adults, and persons with disabilities,” the researchers wrote.

Dr. Damian Caraballo, an emergency room doctor in Tampa, Fla., points out that patients are simply unable to tell the difference between an ovarian cyst, which is usually not life-threatening, and appendicitis, which is. The penalty for being mistaken could amount to hundreds, if not thousands, of dollars. “The last thing I want is for patients to get hosed,” he said.