Q. "We have a 14-month-old daughter (our one and only) who has extreme difficulty sleeping through the night. She's had the problem on and off with teething, colds and so on. Recently it's become a real thorn in our sides. She won't take an afternoon nap any more and typically awakens 5 or 6 times during the night. One night she eked out two hours of sleep. We are becoming worn out and our nerves are thin.

"We've tried rocking, bottles, pacifiers, cuddly toys, nightlights, rubbing her back, letting her cry, letting her get up to "work it out," and bringing her back to bed with us. Nothing has really worked.

"The doctor suggested we just bring her to bed with us for the next couple of months. We certainly don't want to make a habit of that and would rather not bring the crib into our room.

"Naturally we want to be supportive, but we are especially concerned since she is reaching the age when separation gets really tough.

"Any suggestions would be greatly appreciated."

A. Whether a child is quiet or active, she still is meant to be joyous, to learn easily, to feel good.

When she doesn't show these signs, you know that something is wrong and you must try to find the cause. If it can be treated, there won't be any symptoms.

Although the cause in this case probably is minor, the consequences are not. If the anxiety you feel and the sleep you lose continue, they could affect your marriage and shake your self-confidence as parents.

This doesn't mean you should feel defeated. A lot of parents have solved the same problem you have, but not by taking their babies to bed with them.

Call your doctor. Since he hasn't identified the cause yet, you need to find someone who can. Ask him to refer you to the Child Development Center at Georgetown Hospital or the outpatient department at Children's Hospital. You also can make the appointment yourself, if you're embarrassed to ask for a second opinion, but then you won't have your child's records. These can make a diagnosis easier and sometimes the results of recent tests can be used, so you little girl needn't have them again.

She will get a battery of tests though. Expect some to be routine, others to include ones that can't be done in a doctor's office and still more that will be suggested by the case history you and your husband give. That's why you should compile a clear record before you go.

You need to study your baby like a rare specimen (which she is), writing down every illness she has ever had, every symptom you've noticed. It's much easier to recognize a pattern if it's on paper and it will keep you from forgetting something that may seem trivial to you, but will be important to the doctor.

You also should keep a diary of her current behavior, day and night: when she cries, when she sleeps and when -- and what -- she eats. Record where she is and what her toys are. Note the weather each day and how much excitement there was around her, for stress -- good or bad -- can play a part.

Now look further. Does she rub her nose a lot or tickle it with her magic blanket? Does she get dark, puffy or wrinkled circles under her eyes or dry edges around her lips? You'll see these and other pictures in the excellent "Allergies and the Hyperactive Child" by Doris J. Rapp, M.D. (Simon and Shuster, $3.95), one of the most comprehensive books you can find on allergies and the special diets they may require.

One of them is the Feingold diet that is the nemesis of the food industry, the annoyance of many doctors and the last best hope for thousands of parents.

Although scientists usually find the diet can't possibly work, these parents claim that it was the diet's forbiddance of dyes and preservatives -- found in most processed foods, vitamins and medicines -- and salycilates, like aspirin and oranges, that made their children happy and let them sleep through the night.

While some doctors claim that the Feingold list of salycilates is outdated and that any list of them is suspect -- since no one has identified them with real accuracy -- and also that the number of Feingold successes is far overstated, more and more of them are suggesting the diet when all else fails. Certainly, if it could help your child, it would be the cheapest, safest, and in the long run, easiest route to take.

You can call the local association (449-4325) for the time and place of the next introductory meeting, as well as some literature. If you join one of the area chapters (and there are many to accommodate the 2,700 members), a diet counselor will help you learn the "safe foods" and figure out if anything else could be affecting your child, like sugar, wheat, eggs or corn syrup, or perfume, smoke, paint, kapok or those strips of fabric softener you throw in the dryer.

Some of these reactions can be attributed to allergies, but no one knows why dyes and preservatives bother some children and many skeptics deny that they do.

Even so, recent studies show that dyes can send the wrong signals across a brain, perhaps even making a sleepy child stay up half the night (as the Feingold followers say) when she really wants to sleep.

Others challenge this conclusion. But Dr. Ellen Silbergeld, a toxicologist at NIH, has put the controversy into a whole new league Last week she announced the first proof to show that at least one artificial coal tar color has a bio-chemical effect on the brain.

Although the study was done in a test tube, she found that very, very low levels of red dye No. 3 -- used freely in toothpaste, mouthwash, baked goods and candy -- is potent enough to inhibit one of the most basic enzymes in the brain, which controls the transmission of messages.

All of these enzymes aren't affected, however, for this type varies from brain to brain which makes its sensitivity vary also. That's why Dr. Silbergeld believes that there is probably a group of people who can't handle this artificial dye -- and maybe others -- the way some people can't handle milk.

And since this dye gets into all cells (like DDT), at least some of it will reach the brain of anyone who eats it, but because it is so strong, and so prevalent, the enzyme in a susceptible person can't recover from one dose before it gets another.

The trick is to find out how many people react and who they are, but in the meantime you can see if your little girl is affected just by taking the dyes out of her diet.

A risk-free society would be a silly thing to aim for -- and probably no fun at all -- but a child doesn't need to eat dyes that may be unsafe and have no food value, whether they cause symptoms or not.

This may be just another fad, but it won't hurt to give it a try. Thirty years ago people scoffed when some wild medical charges were made, but now there is a warning label on every package of cigarettes sold. eb