Childhood food allergies are a lot less common than people think, according to researchers at the National Asthma Center. The reason so many children are diagnosed as allergic is that someone, usually the parents, "want, for whatever reason, to believe they are," said one of the scientists. "That isn't to say that there aren't children who are allergic to such things as strawberries, tomatoes and chocolate," says Dr. Allan Bock, one of the researchers, "but it is apparently much less common than people think. Bock and a colleague, Dr. Charles May, recently examined 71 children between 3 and 16 who had been thought to have food allergies. Using a double-blind technique, designed to screen out preconceptions by either the tester or the subject, they found that only about 35 percent of the children acutally were allergic. Bock said he thinks family doctors have become accustomed to using "food sensitivity" to explain many digestive problems. When a patient is referred to a specialist, he is usually given a "patch test" in which the skin is scratched and daubled with small amounts of various substances, Bock said. But a reaction to the test means only that the person has antibodies in his system that can react to things in the environment. It does not mean that the substance in question is necessarily causing an allergic reaction. Often, Bock said, a patient whose doctor is looking for a suspect substance hits on one or more that causes reaction in the patch test. The doctor then bans the substance -- food, fur, whatever -- from the person's enviroment. Because so many forbidden substances are food, Bock said, "we see a fair number of children acutally malnourished."