Reye's syndrome, the often-fatal children's disease that follows flu or chicken pox and that has tentatively been associated with aspirin use, is 10 to 20 times more common than doctors have believed, according to a new report in the New England Journal of Medicine.

The disease was thought to occur in only about three children in a million, or about 200 a year in the United States. But eight doctors at the Children's Hospital Research Foundation in Cincinnati reported that, using the most conservative estimate, the disease strikes probably 11 times more children than that. Using a more common estimate, the study shows an increase up to 20 times as great, or about 4,200 cases a year.

According to Peter K. Lichtenstein, one of the authors, doctors have believed that the disease--discovered only 20 years ago--was quite rare and have not been looking for it in patients. Reye's syndrome might often have been diagnosed as some other condition with similar symptoms, he said.

Now that doctors know the disease is more widespread, Lichtenstein said, they are more likely to spot it and use proper treatment.

"We like to think that if we can catch the disease early, we can often prevent it from progressing" to coma and death, said James E. Heubi, another of the Cincinnati researchers.

One theory is that the disease is an infection that prevents the liver from converting stored food into the sugar necessary to run the organs. Repeated vomiting also dehydrates the body. So the theory is that often the disease can be arrested by giving water and sugar intravenously during the critical stage.

Until recent years, it was believed that the Reye's syndrome was fatal in up to 90 percent of the cases, largely because the symptoms were not recognized until the late stages of the disease. But the new study shows that many children apparently get the disease but never reach the worst stages.

Statistical studies have connected the use of aspirin to the disease in some children, but those studies have not been confirmed. The Food and Drug Administration has conducted a campaign to inform parents of the possible connection and is taking comments on a proposed rule that would require warnings on aspirin packages.