Yet interest in the prospect persists. For if the hallucinations, delusions and blunted emotions that disable 40 million people, or 1 percent of the world population, could be ended by plucking an as yet unknown toxin from their bloodstreams, chronic schizophrenics might return to meaningful roles in society.

Dialysis requires a surgical procedure to join an artery and vein in a fistula that can withstand multiple punctures. It takes five to six hours per session for the patient's blood to circulate repeatedly through the machinery, in which time he or she is exposed to the risks of stroke, infection and, in the case of equipment failure, death by loss of blood. If the treatment is not performed at a reputable center, these risks multiply appreciably.

The applicability of hemodialysis in schizophrenia raises the question of how it might be financed for the 2.2 million schizophrenic Americans who perhaps stand to be helped. The Federal Government currently reimburses individuals for hemodialysis in kidney disease at an annual cost of nearly $1 billion. The cost per patient is about $25,000 a year for three treatments a week. Viewed as Experimental

Since fewer sessions are thought necessary in schizophrenia, a course of therapy might begin with one treatment a week for two to six weeks, followed by maintenance dialysis once or twice a month thereafter. At present, however, dialysis is considered an experimental approach to mental illness, not an accepted treatment modality, and insurance companies will not pay the bills.

Scientists have been questioning the therapeutic value of hemodialysis in schizophrenia for more than 20 years, but only recently has the pace of investigation quickened to produce more evidence from a growing number of investigators. And the issue promises to draw even more heated attention in the aftermath of the March 6 Science report, in which researchers at the National Institute of Mental Health said that they had found hemodialysis to be totally ineffective in relieving schizophrenic patients of their hallucinations or other psychotic symptoms. All eight patients failed to improve, while four of them actually worsened in the trials.

''Had it worked, dialysis would have been a tremendous breakthrough in schizophrenia,'' said Dr. Daniel P. van Kammen, unit chief of the Section on Neuropsychopharmacology at the institute and the principal investigator in the study. ''All of us who work with schizophrenics had hoped to find it effective.''

Although the first account of hemodialysis in schizophrenia appeared in a German medical journal in 1960, no verifiable reports were published in the scientific literature until 1977, when Dr. Robert Cade, a kidney specialist in Gainesville, Fla. and the inventor of Gatorade, a drink that replaces body chemicals lost in perspiration, to disclosed how he had treated a hypertensive young woman with dialysis. Improvement Is Described