LOS ANGELES -- The first new drug in 47 years to treat alcoholism has been approved by the U.S. Food and Drug Administration, according to the National Institute on Alcohol Abuse and Alcoholism.


Unlike Antabuse, the currently used drug, which makes the user severely nauseated when he or she uses alcohol, the new substance, called naltrexone, works by blocking both the craving for alcohol and the pleasure of getting high.


"This is the beginning of a new era in alcoholism treatment,'' said Dr. Enoch Gordis, director of the institute, which funded testing of the drug. "This is not a 'magic bullet,' but naltrexone promises to help many patients in their struggle against a chronic, relapsing disease.''


Results from an ongoing clinical trial, which were expected to be released late Tuesday at a New York news conference, indicate that when combined with conventional behavioral modification, naltrexone allows alcoholics to avoid relapse in as many as three-quarters of cases, compared with fewer than half of those who receive counseling alone.


"(We) now have a novel medical approach available that significantly increases abstinence rates and seems to reduce alcohol craving,'' said Dr. Joseph Volpicelli, of the University of Pennsylvania.


Alcoholism is by far the most common drug-abuse problem in the United States. Nearly 11 million Americans suffer from alcoholism, and as many as a third of all Americans are affected by it through a close relative or acquaintance. At least 100,000 deaths are associated with alcohol abuse each year, either from cirrhosis of the liver or from accidents caused by intoxication.


About a million American alcoholics seek help for their problem each year, but many drop out of treatment quickly, in part because their craving for alcohol is so great that they are unable to resist the temptation. Of those who stay in the programs, more than half typically relapse within a few months.


Naltrexone was developed by the DuPont Co., now the DuPont Merck Pharmaceutical Co., for the treatment of heroin abuse, and it was approved for that use in 1984. It targets the same receptors in the brain that produce feelings of pleasure when heroin or other opiates bind to them, but does not itself produce a "high,'' and is not habit-forming.


Although alcohol does not bind to those brain receptors, studies in animals and, now, in humans, show that naltrexone works equally well against it.


Patients who received the drug in trials reported that it reduced the craving for a drink. And because it reduced pleasurable sensations from alcohol, those patients who had a drink or two during recovery were much less likely to suffer a complete relapse.


Two clinical trials reported two years ago studied 70 and 104 alcoholics, respectively. Volpicelli and his colleagues reported that after three months only 23 percent of the people who received naltrexone and behavioral therapy had suffered a relapse, compared to 54 percent of those who received a placebo and counseling.


Dr. Bruce Rounsaville and his colleagues at the Yale University School of Medicine, who used stricter criteria for defining a relapse, found that 39 percent of the naltrexone patients relapsed, compared to 79 percent of those who received only counseling.