A consumer advocacy group yesterday asked the Food and Drug Administration to ban the only drug approved in the United States for treatment of Alzheimer's disease. The group cited evidence, from a study sponsored by the drug's manufacturer, that it does not work for Alzheimer's and may even make the condition worse.

Public Citizen's Health Research Group made the request in a letter to FDA Commissioner David Kessler. The drug is ergoloid mesylates, which is most often sold under the brand name Hydergine, a product of Sandoz Pharmaceuticals. Other companies sell drugs containing the same ingredient under the names Gerimal and Niloric.

In 1989 patients and their insurance plans spent nearly $42 million on prescriptions for the drug, according to figures from the National Prescription Audit. This was spent on 696,000 prescriptions at an average price of $60 each.

FDA spokeswoman Eva Kemper said the agency had not received the letter and could not respond. But a Sandoz official said the company stands behind the drug as a treatment for Alzheimer's and other kinds of mental deterioration in older people.

Alzheimer's is a progressive, irreversible neurological disorder that most often strikes the elderly. Symptoms include gradual short-term memory loss, impairment of judgment, disorientation, personality change, difficulty in learning and loss of language skills.

No cause or cure is known. Hydergine is claimed to slow the progress of the ailment.

Health Research Group based its request to the FDA on a six-month study by two researchers at the University of Colorado School of Medicine in Denver. Their results were published last August in the New England Journal of Medicine.

The researchers studied 80 Alzheimer's patients, giving half Hydergine and the others placebos.

"We found that those who got the active medication were no better off than those who got the placebo in any way," said Christopher Filley, a University of Colorado neurologist and one of the researchers supported by the Sandoz Research Institute. The second researcher, Troy Thompson II, is now with the Jefferson Medical College in Philadelphia.

David Winter, vice president for scientific and external affairs at Swiss-owned Sandoz, said more than 50 other studies in Hydergine's 30-year history had shown positive results in patients. "One negative study in the face of 50 positive ones scarcely changes our position on it," Winter said.