My son is almost 17 months old and he hasn't begun talking yet.

I realize it's too soon for him to be constructing sentences but he can't even say Daddy or Mommy. He doesn't verbalize at all.

He does make lots of shouting and grunting sounds and he's extremely active and well-coordinated for his age (he began walking at 9 months). He has absolutely no fear about climbing and jumping.

Some people have told me that his motor skills are developing faster right now and he'll make up for his lack of verbal skills later.

I've heard lots of stories about kids who didn't talk until they were 3 and then began speaking in complete sentences. Still, it's a little frustrating to see other children saying names and reciting numbers. Should I be worried? Is there anything I can do? I've tried reading books to him, but he has no attention span for it; he just squirms out of my lap and runs away.

My husband and I both work full-time and our son is with a sitter most of the day. Could this be the reason?

If a child isn't talking by 17 months, there is some cause for concern. According to Dr. Patricia Larkins of the American Speech-Language-Hearing Association, children usually say a few words like "mama," "daddy" and "bye-bye" at a year and have a 50-word vocabulary at 17 months. This isn't absolute, of course. There is a great variety between children and between the sexes: girls talk sooner than boys.

Some of the language delay could come from the sitter, if she doesn't speak to your son slowly enough for him to understand, or often enough, or if she shushes him when he tries to talk or if she simply doesn't respond to his sounds. A child learns to talk much quicker (and feels much better about himself) if someone congratulates his attempts and repeats them back to him as well-enunciated words. Reinforcement makes all learning easier.

Your child's language problem also could be compounded if he seldom plays with other children or if you and your husband take such good care of him that you anticipate his every need, so he doesn't have to try to tell you what he wants.

You can test this by turning his requests into a game.

If he points to the bottle, hand him the toy that's next to it. He points again and you hand him the book, and again, and you give him some water. Just before he screams in frustration, you say, ''Oh, the BOT-TUL!'' and say ''bottle'' like that several times, with your face just inches from his. Some children can be taught the simplest words as early as a few months with this face-to-face technique, because they see how the mouth, the teeth, the tongue and the lips work together -- and because they find imitation so irresistible.

You also want to consider a hearing problem -- a major cause of delayed speech. For a simple test, turn around and quietly say his name or ask if he'd like a cookie or a walk. If his hearing is good, he'll give some sign. Even if he does respond, you'd be wise to have him evaluated by a speech-language pathologist.

A hearing problem can be as simple as a blockage in the ears or the result of chronic middle ear disease. When this is painless -- and it can be -- the problem may go unnoticed. He also could have damage or an abnormality in the middle or inner ear and for these and other reasons he would find it hard to distinguish sounds or hear the higher frequencies.

If a hearing impairment is suspected, the speech-language expert usually sends the child to an audiologist to verify the loss and measure it. This is harder than it sounds. Although the pediatrician can spot a profound loss even in a very young baby, the child with a lesser loss can be a puzzle for years.

The audiologist will then send the child to an otologist, if the problem can be treated medically or surgically, or may fit your son with a hearing aid. This not only can make up for a conductive hearing loss but correct the so-called ''nerve deafness'' of the inner ear. Moreover, today's devices are so tiny, and so well-regulated, that even a 3-month-old baby can be fitted.

If your child's hearing isn't impaired (or even if it is), the speech-language pathologist will conduct other tests in the initial one- to three-hour assessment. He or she will test your son's ability to process language by giving him both verbal and non-verbal directions and study the way his mouth is built to make sure that speech can come easy. The child who can't stick out his tongue, for instance, may have to have the membrane clipped beneath it.

Also to be considered will be the way the child acts with the sitter and at home. If either situation might cause or contribute to the problem, the language pathologist may work with your child, either individually or in a group, or have him go to nursery school for six to 12 months, to be with other children.

It may be that your child is simply one of those live wires who's still too busy to talk. Nevertheless, an examination won't hurt. You can't solve a problem until you know what it is or if it really exists.

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