Q. "My little boy Jon, who is 6, gets sick so much," writes a mother in Wheaton. "Even when he's well he often acts tired and listless, and grumpy, too. Until he started first grade I never realized how much more fun other kids seemed to have.

"Jon misses so much school with his tonsillitis and his ear infections that the pediatrician says maybe he should see an allergist. What are we getting ourselves in for?"

A. If Jon is allergic, you're already in for it. But you can't take care of a problem until it's identified -- especially allergies.

More and more doctors are recognizing that allergies can cause a number of chronic problems, both physical and behavioral, and they come from the oddest places: from your best perfume to the fumes given off by plastic bags; from peanut butter or jelly to chocolate ice cream. It takes a real expert to find out.

Since you want the best for your child (and what mother does not?) and since a good diagnosis costs less money and less travail than a bad one, you need to shop as wisely for this magician as you would for a mink coat. Just be glad he won't cost as much.

Your chances of getting a first-class specialist improve markedly if you get one who is board-certified, with university or research connections. These are signs that he probably is knowledgeable, well-respected by his colleagues and is keeping up with his field.

The practitioner who gives tests with a regional pollen kit and sends away for the results is miles out of this league, for it is the case history that an allergist relies on the most.

That's why he will spend so much time finding out if allergies run in the family and if Jon had rashes as a baby. He will want to know when his illnesses began and when they occur, to see if they are caused by the weather or the season.

He also will ask you about the rug in his room, the animals in the house (both stuffed and live) and what your child eats every day, for these are often the clue to year-round problems.

If your child is allergic, he has developed special antibodies to substances he has met before. When they meet again, he releases histsamines into his smooth muscles, which are threaded through the body. The reaction may affect one area or another: the shock organs, as they're called. This may be the skin, eyes, ears, the bronchial tree, digestive system, the central nervous system, or a combination. So you can see why your pediatrician suspects allergies.

To identify allergies, Jon will be given tiny, individual doses of perhaps several dozen substances, probably under the skin, to make sure they get into the system. Any reaction shows at each of the needle sites.

Dr. Stanley I. Wolf, a pediatrics professor at George Washington University and assistant director of allergy at Children's Hospital, feels these tests are about "50 percent accurate."

A reaction, he says, shows that the child has made a lot of antibodies to a particular substance, "proving that the person has been allergic to it in the past, but that it's over; that he is allergic now, or that he may become allergic."

Because allergies come and go, a doctor will depend more on the interview. If he can find out what Jon is exposed to, he may figure out the cause. If it's necessary to better identify a food, he will put the child on a diet and then have him eat the food not once, but several days in a row.

There are three ways to handle an allergy, says Dr. Wolf -- avoidance, medicine and injection therapy.

"You can change the environment. If the person is allergic to mold, the houseplants go. There i mold in the soil," he says. "If the mattress and pillows are old, they get covered with an allergy-proof casing. If the child reacts to peanut butter -- a potent allergen -- he will have to avoid it for maybe six months, then try it again."

An electronic precipitator may be ordered to remove pollutants from the air at home, or if ragweed is a factor, the family perhaps can go to the beach for their vacation during the second two weeks of the ragweed season when it is at its worst, so the wind can blow away much of the pollen.

For the seasonal allergy that can't be avoided, he prescribes medicine. For chronic cases where neither avoidance nor medicine are enough, he makes up a serum, a necessity in nearly half of his patients, adult and children.

The serum is made of those substances that bother a child and it is given, usually by the pediatrician, in increasing doses, so he can build resistance to them, as with a vaccine.

Dr. Ellis April, the emeritus chief of the allergy section at Washington Hospital Center and assistant professor emeritus of clinical medicine at Georgetown University, advocates injection therapy for most of his patients (since many inhalants are so hard to eliminate), as well as avoidance, precipitators, medicine and even hot liquids. Patients with respiratory or digestive reactions are told to drink something hot first thing in the morning, during the day and last thing at night, to melt mucous blocking the sinuses and prevent postnasal drip.

If your specialist finds your son to be one of America's 3 million allergy victims, you probably will find yourself deluged with more information than you can absorb at once. For this we suggest membership (cost, $6) in the D.C. chapter of the Asthma and Allergy Foundation (424-6617), so you can learn how other parents handle the problems.

This is the group that negotiated to get major allergens out of Montgomery County public schools. Their rules have been copied throughout the country. The chapter publishes four newsletters a year and a calendar (Allergy Tips, $3) with some of the best recipes for allergic children. Among other excellent information: the name of a place that sells those mattress covers: Allergen-Proof Encasings, Inc., P.O. Box 5236, 1450 E. 363rd St., Eastlake, Ohio 44094.

The chapter sponsors four talks a year by well-known allergists. Dr. Wolf, also co-director of the Allergy Center in Silver Spring, and Maryland allergists Dr. Dennis Cleban and Dr. Solomon Barr will speak at the next one: at 7:30 p.m. Wednesday at Charles Woodward School on Old Georgetown Road in Bethesda.

Q. "Now that spring has practically sprung, I'm eager for my 9-year-old to learn something new, so he'll quit thinking that television is the answer to everything.

"Jerry is pretty smart, in the fourth grade and he's good at making things, but he's in such a rut," writes a McLean mother.

A. You're in luck. The National Park Service starts its classes soon at Glen Echo Park, home of the Adventure Theater in the Palisades. It's a beautiful place that began as a church meeting ground and turned into an amusement park, so there are classes in the Chatauqua Classroom (among other places) and, in the summer, there's a carrousel to ride.

Nearly 100 classes will be offered, starting as early as April 2, and a dozen are for children as young as 5.

Jerry might like the photography classes, or sculpture or architecture, but there is weaving, writing, drama and dance, as well as two offbeat classes: one for children to make native American Indian games and another in Quiltmaking for parents and children.

Pre-registration has already started. To find out more, call Glen Echo (492-6282) between 9 a.m. and 5 p.m. weekdays and from noon to 6 p.m. Saturdays.