For years, doctors have known that women get drunk faster than men. Now, a new study suggests that women may react more quickly to liquor because they are far less able to break down and digest the alcohol before it circulates in their blood system and goes to the brain.

The report, published in the current issue of The New England Journal of Medicine, provides the first biological evidence that may help explain one of the more unusual differences between the sexes.

The key is an enzyme in the stomach called alcohol dehydrogenase that breaks down alcohol before it enters the bloodstream. The researchers, from the University School of Medicine in Trieste, Italy, and the Veterans Affairs Medical Center in the Bronx, reported that the stomach lining in women manufactures smaller amounts of this enzyme than does the stomach lining in men.

As a result, women may be less able to digest the alcohol before it reaches the bloodstream, where it can then travel to the brain and the liver.

The new findings also help explain why female alcoholics suffer more liver damage than men do, and why they develop other adverse effects of alcohol more quickly than do male alcoholics.

The study, which involved 43 people, is considered preliminary, and more research is needed to define more precisely this apparent biological difference between men and women. But if the results prove accurate, health officials who are charged with setting appropriate levels of alcohol consumption for driving, operating machinery and other activities that require coordination may have to consider sex differences when they make regulations governing alcohol use.

Most people who have experience with liquor have known for years that, when size and weight are taken into account, women usually have higher blood-alcohol levels than men who drink exactly the same amount.

Scientists had several theories to explain that difference, but the most common was that because women have less water in their tissues than men have, they would have a higher concentration of alcohol.

That now appears to be wrong -- at least in part. Because women have less of the critical enzyme, more alcohol from every drink enters their blood in its pure form. Just why women produce less amounts of the enzyme than men is not known, and researchers said that other studies would have to confirm their findings.

According to their report, even after accounting for differences in body weight, almost a third more alcohol would enter the bloodstream of a woman than of a man. That means a woman would get drunk on about 30 percent less liquor than would be required for a man.

The differences are much more significant if weight is not considered a factor. The researchers said that drinking sustained over years dramatically reduces the ability of men to break down alcohol in the stomach. But it appears to eliminate women's ability to digest liquor altogether.

The researchers discovered several years ago that the enzyme alcohol dehydrogenase could be found in the stomach linings of men. They then split groups of men and women into those who were alcoholics and those who were not. There were six women and six men who were alcoholics. There were 14 men and 17 women who were not.

The researchers tested them regularly for concentration of alcohol in their bloodstreams and also for the amount of the key enzyme they had in the linings of their stomach. The researchers administered carefully measured doses of alcohol before making their measurements to assure consistent results.

The doses were adjusted for height and weight, and they were the equivalent of the alcohol in 1 1/2 drinks in the hour after a meal, about an ounce and a half for a 110-pound woman and two ounces for a 154-pound man. The researchers said one drink was defined as a 12-ounce beer, a four-ounce glass of wine, or a 1 1/2-ounce shot of 80-proof liquor.

For both the alcoholic and non-alcoholic groups, "women had higher blood ethanol concentrations than men after ingesting an equivalent" amount of alcohol, the authors wrote. By comparison, there was no real difference between the sexes when the ethanol was given intravenously, in which case the alcohol bypassed the stomach and went directly into the bloodstream.

The missing enzyme helps explains another important mystery: Why female alcoholics often have much more severe and early liver disease than men. The researchers speculate that without adequate amounts of the crucial enzyme, women completely lose their defense system in the lining of the stomach. As soon as they start drinking, the destructive effects of alcohol are more likely to begin because they are getting so much more pure alcohol into their blood and to their liver for a longer period of time.