Q. My sister-in-law recently had a little girl after having two boys, now 5 and 2 1/2.

Her daughter has a defect in her spinal column called spina bifida and is expected to have limited use of her legs. She probably will be able to walk with the help of braces and crutches, but both feet are permanently paralyzed. The doctors say she also will be prone to respiratory infections and must be protected from catching colds, etc.

At the same time the mother wants her child to grow up as normally as possible and to the fullest capacity. She would like any suggestions to keep her from crippling her daughter emotionally and still take the precautions necessary.

A. One baby in 1,000 is born with spina bifida--a spinal column that didn't close properly. This makes it the most common of all severe birth defects, more prevalent than muscular dystrophy, multiple sclerosis, polio and cystic fibrosis combined.

Although the spine is closed surgically after birth, the child still is affected by the nerves in the spine that didn't form properly in the womb. This may cause many problems, such as hydrocephalus, kidney or bowel trouble, or it may affect the motor skills, depending upon which vertabrae are involved. Although most of these children require braces and crutches, they now have a normal life expectancy and four out of five have a normal I.Q.

They do require extra protection, of course, but usually not as much as they get.

Most children with spina bifida are overprotected, says Dr. John M. Freeman, director of the Birth Defects Clinic of Johns Hopkins in Baltimore. "You do for them as babies, and then it's easier to keep doing for them. You must be very careful to be supportive without being overprotective."

Like any child, your niece needs to be trusted to do as much for herself as possible, even as young as she is. Any baby has the right to stretch for something that's a little hard to reach, just as she can babble for what she wants. These small accomplishments build self-esteem and the daring to try for more.

Because these children usually have multiple problems, Freeman feels it is important for your niece to be treated in a birth-defects clinic, rather than taken from doctor to doctor. Too much shuffling around might invite conflicting treatment, and it would be exhausting for everyone. It also could make the family view the child as an invalid, and the child would do the same.

Birth-defect clinics, fairly common throughout the country, have similar setups.

At the Baltimore clinic there is a pediatrician, pediatric neurologist, neurosurgeon, orthopedist, urologist, nutritionist, psychiatrist, occupational therapist and a physical therapist so the child--and her family--is treated with a comprehensive approach.

Here the family learns how to take care of their child's special needs while still treating her as normal, within the framework of her problem. This helps her friends and neighbors do the same. Parents also are encouraged to give enough attention to their other children, so they don't get resentful.

As your niece gets older she should have her share of the family chores and sports. While the boys may play soccer and baseball, they also can play crocquet and archery with their little sister, so she knows she's part of the gang. Swimming is good also, and so is horseback riding if it can be afforded. An ability in sports gives children a terrific sense of pride, which these children especially need. The Special Olympics is a great help here, at least on the local level, where it's not so competitive.

While your in-laws will get the most professional support from a clinic, they also need other support from other parents in the same situation.

Have your sister-in-law contact The Spina Bifida Assn. of America, Suite 317, 343 S. Dearborn St., Chicago 60604 (800-621-3141). It's a good, young, legitimate organization with 99 chapters around the country. It's in the local groups that parents share their solutions as well as their griefs and fears. This is particularly important.

Any child stresses a marriage, but a handicapped child stresses it much more and either pulls the parents further apart or draws them closer together, depending on how the problem is handled. Counseling from other parents, and from doctors in the birth-defects clinic, could make your sister-in-law's marriage stronger than ever.

You and all the relatives can help by treating your niece with the same respect you treat the most able child. Since spina bifida has affected her lungs, which is unusual, you'll have to keep away when anyone in your family has a sign of a cold. Otherwise, she should be one of the gang, with all the cuddling and scrapping and fooling around that goes with it.

This doesn't mean that your niece is just like any other child. She will present a lifetime of differences, some of which will be harder for others to take than they are for her.

She will teach you about compassion but not pity; courage but not foolhardiness; strength but not aggression. And above all, that a handicapped child's spirit can overshadow a disability.

Questions may be sent to Parents' Almanac, Style Plus, The Washington Post.