The Trump administration is proposing huge changes in the way Medicare pays doctors for the most common of all medical services, the office visit, offering physicians basically the same amount, regardless of a patient’s condition or the complexity of the services provided.

Administration officials said the proposal would radically reduce paperwork burdens, freeing doctors to spend more time with patients. The government would pay one rate for new patients and another, lower rate for visits with established patients.

“Time spent on paperwork is time away from patients,” said Seema Verma, the administrator of the Centers for Medicare and Medicaid Services. She estimated that the change would save 51 hours of clinic time per doctor per year.

But critics say the proposal would underpay doctors who care for patients with the greatest medical needs and the most complicated ailments — and could discourage some physicians from taking Medicare patients. They also say it would increase the risk of erroneous and fraudulent payments because doctors would submit less information to document the services provided.

Medicare would pay the same amount for evaluating a patient with sniffles and a head cold and a patient with complicated Stage 4 metastatic breast cancer, said Ted Okon, the executive director of the Community Oncology Alliance, an advocacy group for cancer doctors and patients. He called that “simply crazy.”

Dr. Angus B. Worthing, a rheumatologist, said he understood the administration’s objective. “Doctors did not go to medical school to type on a computer all day,” he said.

But, he added: “This proposal is setting up a potential disaster. Doctors will be less likely to see Medicare patients and to go into our specialty. Patients with arthritis and osteoporosis may have to wait longer to see the right specialists.”

Private insurers often follow Medicare’s lead, so the proposed change has implications that go far beyond the Medicare program.

The proposal, part of Medicare’s physician fee schedule for 2019, is to be published Friday in the Federal Register, with an opportunity for public comment until Sept. 10. The new policies would apply to services provided to Medicare patients starting in January.

“We anticipate this to be a very, very significant and massive change, a welcome relief for providers across the nation,” Ms. Verma said, adding that it fulfills President Trump’s promise to “cut the red tape of regulation.”

“Evaluation and management services” are the foundation of an office visit. Medicare now recognizes five levels of office visits, with Level 5 involving the most comprehensive medical history and physical examination of a patient, and the most complex decision making by the doctor.

Level 1 is mostly for nonphysician services: for example, a five-minute visit with a nurse to check the blood pressure of a patient recently placed on a new medication.

A Level 5 visit could include a thorough hourlong evaluation of a patient with heart failure, chronic obstructive pulmonary disease, high blood pressure and diabetes with blood sugar out of control.

“The differences between Levels 2 to 5 are often really difficult to discern and time-consuming to document,” said Dr. Kate Goodrich, Medicare’s chief medical officer.

Medicare payment rates for new patients now range from $76 for a Level 2 office visit to $211 for a Level 5 visit. The Trump administration proposal would establish a single new rate of about $135. That could mean gains for doctors who specialize in routine care, but a huge hit for those who deal mainly with complicated patients, such as rheumatologists and oncologists.

For established patients, the proposal calls for a payment rate of about $93, in place of current rates ranging from $45 to $148 for the four different levels of office visits.

“This proposal is likely to penalize physicians who treat sicker patients, even though they spend more time and effort and more resources managing those patients,” said Deborah J. Grider, who has audited tens of thousands of medical records and written a book on the subject.

Dr. Atul Grover, the executive vice president of the Association of American Medical Colleges, said, “The single payment rate may not reflect the resources needed to treat patients we see at academic medical centers — the most vulnerable patients, those who have complex medical needs.”

While the proposal would redistribute money among doctors, it is not intended to cut spending under Medicare’s physician fee schedule, which totals roughly $70 billion a year.

If the new rules really do simplify their work, doctors say, they will be elated.

“We can focus more on patient care and less on the administrative burden of documentation and billing,” said Dr. David B. Glasser, an assistant professor of ophthalmology at the Johns Hopkins University School of Medicine. “We sometimes joke that it can be more complicated trying to get the coding level right than it is to figure out what’s wrong with the patient.”

But, Dr. Glasser said, the financial impact of the proposal on eye doctors is not yet clear.

Documentation requirements have increased in response to growing concerns about health care fraud and improper payments that cost Medicare billions of dollars a year.

In many cases, federal auditors could not determine whether services were actually provided or were medically necessary. In some cases, they found that doctors had billed Medicare — and patients — for more costly services than they actually performed.

In a report required by federal law, officials estimated early this year that 18 percent of Medicare payments for office visits with new patients were incorrect or improper, about three times the error rate for established patients.

To prevent fraud and abuse, Medicare officials have repeatedly told doctors to document their claims. “If it is not documented, it has not been done” — that is the principle set forth in Medicare’s billing manual for doctors.

The Trump administration is moving away from that policy.

“We have proposed to move to a system with minimal documentation requirements for Levels 2 to 5 and one single payment rate,” Dr. Goodrich said.

Doctors now must provide more documentation for higher levels of care. Under the proposal, “practitioners would only need to meet documentation requirements currently associated with a Level 2 visit.” That would reduce the need for audits to verify the level of office visits.

Medicare officials acknowledged that doctors who typically bill at Levels 4 and 5 could see financial losses under the proposal. But they said some of the losses could potentially be offset by “add-on payments” for primary care doctors and certain other medical specialists.

With such adjustments, Medicare officials said, the impact on most doctors would be relatively modest. A table included in the proposed rule indicates that obstetricians and gynecologists would gain the most, while dermatologists, rheumatologists and podiatrists would lose the most.