Q: My day-care provider reports that my son, 2 years and 8 months old, is very hard to live with.

He tests her constantly, bullies other children, sulks, interferes with other kids' activities and is negative about almost everything. He wants his own way and resists any and all efforts at direct control. He is wearing her out fast.

I returned to work part time so I could get a break from him for half the day, as he has been this way since he was a baby. My first sitter burned out after a few months and he was utterly miserable at a day-care center.

He gets so much negative attention for his behavior that it must affect his self-concept and make matters even worse.

I've read every book on the subject and tried every technique they suggest, but with no lasting effect. My husband and I are at our wits' end.

We love our son and even respect his strengths, but he has to learn to get along with others and accept reasonable restrictions. It seems as if he thrives on confrontation.

He's otherwise very healthy, bright, a good eater and sleeper. What do you suggest?

A: When 2-year-olds are terrible, age is often the culprit.

Your child's need for independence is clearly very strong, but every child has that need. It usually shows up at 15 months, escalates at 18 months, gets intense around the second birthday and often reaches extraordinary levels between 26 and 30 months, when parents may feel totally inadequate.

They begin to get their confidence back as the child's behavior quiets around 32 months, especially if they have child-proofed the house; used diversion to say no as often as possible (since challenges make most children more obstinate at this age); given their child spontaneous hugs and "I love yous" for good behavior; and ignored most of his tantrums -- all classic techniques to avoid confrontations with the terrible, terrific 2, so they don't become a way of life at 3.

Because your little boy has always been difficult, however, you should look for an underlying cause.

Although he is seemingly healthy, such exaggerated behavior is often caused by allergies. They can attack any part of the body or the brain, causing chronic physical or emotional problems. And if the reaction is chronic, so are the encounters.

More and more doctors recognize that something in a child's environment or diet can cause earaches, joint aches, bed-wetting -- and poor behavior. These symptoms can include hyperactivity (or hypoactivity, which seldom bothers parents); anger; tension; anxiety.

Even a breast-fed baby may get colic in reaction to the milk and other foods his mother eats. Milk, eggs, wheat, corn, legumes (including peanuts), pork and chocolate are the most common food offenders at all ages and they also can include something he smells or touches.

Not all food reactions are caused by allergies. Some doctors believe the molecular structure of artificial dyes or preservatives, like BHA and BHT, and sometimes of salicylates such as oranges, apples and aspirin, can make them toxic to children and cause the symptoms you describe.

Parents, however, don't care what causes a problem, they just want it to go away.

A pediatric allergist can tell you if kapok, feathers, dog hair, dust or mold bother your child, so you can take the substance out of his environment and give him medicine when he can't avoid it.

Most allergists, however, only believe in those food allergies that show up in an intradermal test or a test tube. Unfortunately, only one type of food allergy -- the kind that produces hives and asthma -- can be measured in these ways, according to Dr. James Breneman, former head of the food allergy committee of the American College of Allergists. There are three other kinds that don't show up for two to three days.

You can test for food reactions yourself. Let your child eat only a few plain foods, preferably those he seldom has and that are the least allergic -- lamb, chicken, rice, pears, bananas, olive oil. Give him only these foods for five days.

If he's still difficult, he's either allergic to one of these few foods or to a nonfood. Or the problem is caused by something else.

If his behavior is markedly better after five days, however, he's probably bothered by something you've taken out of his diet. Give him his favorite food and watch his behavior for two days. If he's worse, cut it out of his diet. Repeat this technique over and over every 48 hours until you've tried everything he eats. You can offer these foods again, one at a time, in about six months, to see if he has outgrown the reaction, but he still may only be able to eat it every four to five days.

This is a big bother, but not as much as his current behavior, nor as hurtful. If it continues it will damage his self-esteem -- every child's greatest asset.

Questions may be sent to P.O. Box 15310, Washington, D.C. 20003.