The Institute of Medicine on Tuesday proposed a new name and new diagnostic criteria for the condition that many still call chronic fatigue syndrome.

Experts generally agree that the disease has a physical basis, but they have struggled for decades to characterize its symptoms. The new report may help improve diagnosis, but the recommendations are unlikely to end the long, contentious debate over who has the condition and what may be causing it.

An institute panel recommended that the illness be renamed “systemic exertion intolerance disease,” a term that reflects what patients, clinicians and researchers all agree is a core symptom: a sustained depletion of energy after minimal activity, called postexertional malaise.

The new name “really describes much more directly the key feature of the illness, which is the inability to tolerate both physical and cognitive exertion,” said Dr. Peter Rowe, a member of the panel and a pediatrician at Johns Hopkins who treats children with the condition.

An alternate name for the illness, myalgic encephalomyelitis, meaning “brain and spinal cord inflammation with muscle pain,” was coined decades ago. Many experts now refer to the condition as M.E./C.F.S.

About one million people in the United States are believed to have the syndrome. Many say they have been accused of imagining or exaggerating their symptoms, and many doctors have long viewed it as a psychological illness.

The authors urged that doctors take patients’ physical complaints seriously. “This is not a figment of their imagination,” said Dr. Ellen Wright Clayton, the chairwoman of the Institute of Medicine panel and a professor of pediatrics and law at Vanderbilt University.

Patients attribute much of their mistreatment to the name “chronic fatigue syndrome,” chosen by the Centers for Disease Control in 1988.

“We wanted to move it away from this label that often elicits very trite comments, possibly intended to be humorous, like ‘I’m tired, I must have that too,’ ” Dr. Rowe said. “Everybody’s had some experience of fatigue, but this is so much more than that.”

Leonard A. Jason, a psychology professor at DePaul University in Chicago and an expert on the illness, predicted that patients would be reluctant to accept the new name.

“The committee has come up with a name without vetting it,” Dr. Jason said. “And they will basically get a tremendous amount of discontent and dissatisfaction right from the starting point, because the patients want something very different.”

Many strongly prefer myalgic encephalomyelitis, because it underscores a physical basis for the condition. But the authors of the new report said that myalgic encephalomyelitis “does not accurately describe the major features of the disease.”

Although some research has suggested that inflammation of the central nervous system is involved, its role is not proven, and muscle pain is not as prominent as other features.

Most patients develop the syndrome after contracting a cold, flu or other viral illness, but other environmental or toxic exposures may act as triggers. Although no cause has been identified, people with the illness may suffer neurological, hormonal and immunological impairments.

The new diagnostic criteria include six months of profound, unexplained fatigue and postexertional malaise, as well as a third key symptom: unrefreshing sleep. Patients must also exhibit cognitive problems or “orthostatic intolerance,” an inability to stand upright for more than a short period.

“We are hoping they provide a very clear path for clinicians to make a diagnosis,” said Dr. Lucinda Bateman, a panel member from Salt Lake City. “We want to make sure that symptoms that maybe have been overlooked by clinicians have been put front and center.”

Developing diagnostic criteria is easiest when medical tests can be used, as with HIV or hepatitis C, and much harder when an illness must be defined by its symptoms. Researchers and clinicians have developed at least 20 different definitions over the years for the condition.

The most commonly used has been the C.D.C.’s definition, but many researchers and clinicians complain that those criteria identify many patients who more likely are suffering from depression and other conditions that can cause prolonged fatigue.

The new report is one of two studies that have been the focus of intense debate among patients with the condition. The National Institutes of Health is currently revising a draft report about research priorities for the illness.

Patients have criticized both efforts. Although the 15 members on the Institute of Medicine panel included some clinicians with strong experience in treating patients with the condition, a majority were not known to have any expertise in the illness.

In recent years, the National Institutes of Health has spent around $5 million a year on research for the condition, far less than patient advocates would like.