CHARLOTTE, N.C. (AP) _ A blood test has been devised to help doctors diagnose chronic fatigue syndrome, a flu-like illness some have dubbed ''yuppie flu,'' a scientist said Sunday.

Dr. Jay Levy of San Francisco announced the development at a national conference on the disease here. He predicted the mysterious illness will be the ''disease of the '90s'' as the public and the medical community become more aware of it.

''It takes about decade before the public wakes up and realizes that this is not going to go away,'' Levy said.

The weekend conference, titled ''Unraveling the Mystery,'' drew 400 people including researchers and people afflicted with the ailment.

Chronic fatigue syndrome is characterized by fatigue, exhaustion, joint and muscle aches, and an array of other problems that persist for more than six months, and often for years.

Tens of thousands of Americans believe they have chronic fatigue syndrome, although the extent of it is uncertain. Some researchers believe the disease may be centuries old and it's just been misdiagnosed all this time.

Because it has been widely reported among well-educated women in their 30s and 40s, the syndrome was dubbed ''yuppie flu.''

An effort to discover how widespread it is, an inter-agency coordinating commmittee has been formed, said Dr. Walter Gunn, a chronic fatigue syndrome researcher at the Centers for Disease Control in Atlanta.

Levy, an AIDS researcher at the University of California at San Francisco, led a group that developed a blood test for the disease.

Levy said his team was unable to find one virus that caused the illness. Some research has linked the syndrome to a retrovirus, one of the family of viruses that causes AIDS.

''Because of the immune profile of these patients, we believe there has been an infection by some agent, though this agent may no longer be in the body,'' Levy said. ''Or it may be hidden. It cannot as yet be identified.''

In any case, he said, the immune system of chronic fatigue patients is activated for months or years, creating high levels of a particular white blood cell, caled the CD8+ cytotoxic T cell.

The persistence of the white blood cell causes symptoms of a viral infection, Levy said.

The CD8+ cytotoxic cells appear to be the major cell type activated in the disease - a signature unique to chronic fatigue syndrome, Levy said. So the blood test checks for high levels of those cells.

''This is a way to distinguish those with fatigue alone from those with an immune reaction that causes chronic fatigue,'' he said.

Levy said the level of the white blood cells along with an examination of the patient's medical history could determine whether a patient is suffering from the syndrome.

Levy and other researchers suggested the syndrome be renamed ''chronic immune activation syndrome'' to reflect their findings.