Q. My sister just had her first baby, two months early.He is an ounce shy of four pounds, and, it seems, healthy, but we're quite worried. Is there anything we can do to be helpful?

A. Be patient. Stand fast. Send flowers. Visit. New parents need the uncompromising support of their family and friends, but parents of premies need it even more.Your attention won't be an intrusion, unless you ask scary questions they can't answer -- like "Will he live?" and "Is he retarded?"

Your sister and her husband are having a hard enough time living with their own fears; they don't need yours too.

Actually, the problems are much easier to handle today. Premature babies have an astonishing track record now, even though some have weighed less than a pound at birth and lived in the womb only 23 weeks. Hospitals are saving 75 percent of those who weigh less than 3 1/2 pounds, and 95 percent of those who, like your nephew, weigh between 3 1/2 and 5 1/2 pounds. Not only that, there are relatively few serious problems later.

Much of this success is due to the careful demarkation between the true premies -- who are born at least three weeks early and weigh less than 5 1/2 pounds -- and those who are tested and found to be full term but have a low birth weight, usually because the mother had some health problem.

The premies are hatched too soon and the tinies are born too small; each is likely to have different problems and different treatments. The full-term, low-birth-weight babies may have birth defects or disorders, while the premies are more likely to have trouble nursing and swallowing -- which take both energy and coordination -- and even crying, which also takes much effort. Their systems are so immature they also may have difficulty with their breathing or their circulation; the lungs and the brain are the last organs to develop.

Whatever the problem, these babies are nurtured in neonatal intensive care units (NICU) of extraordinary sophistication. There are dozens of futuristic inventions to keep them safe, and a crackerjack team of doctors and nurses.

There is a sense of loss, however, when a pregnancy is cut short. The baby has lost two months of growing but the parents have lost two months of their growing sense of parenthood, their bonding as a family. With this can come the anger, guilt and depression of grief: a sense of unfairness and "what did we do wrong?" Your sister needs your good cheer to combat this gloom, to listen to her concerns, but not to mirror them.

She needs your encouragement on many levels, such as breast feeding, which is better for her baby and for her. This is one of the ways you can help her realize that while the baby needs the doctors and nurses, there are some things a mother does best.

You probably will help her most if you emphasize the importance of her voice and her husband's. Because a premie is subjected to so many procedures, he especially needs to hear the voices he heard for months in the womb. The more your sister and brother-in-law are allowed to feed, bathe and change their baby -- and talk to him -- the more he's likely to thrive.

Even if they aren't allowed to take some physical care of the baby, they can croon over him and reach into the incubator and stroke his legs. You can help there by doing as much of their cooking and shopping as you can, so they can spend more time with him. This will alleviate their anxiety as much as his.

You might even ask if their NICU occasionally plays parents' voices on a small tape recorder in the isolette, which you could provide and tape for them. Studies show that stimulated babies are usually more alert, react better and are consoled more easily than babies who aren't given much stroking or conversation.

For your sister's stroking -- and if you can by only one book -- get Your Premature Baby by Robin Marantz Henig, written with Dr. Anne B. Fletcher, chief of the neonatology unit at Children's Hospital (Rawson Associates, $14.95). It's sensitive, practical, thorough and first-rate. For the support that comes from other mothers who have been there, the book Premature Babies by Sherri Nance (Arbor/Priam, $8.95) should help her deal with the deep and special emotions born with her baby.

Your sister also will need a good deal of practical help to get the nursery ready and to prepare the layette. There are those who want to postpone this until they're sure the baby is out of danger, but this seems pessimistic. Better to dismantle a crib than be afraid to prepare it.

A sheepskin is one of the best layette gifts for any baby, especially a premie. A Cambridge University study found that premature babies who slept on them gained more weight, rested better and lost less body heat than those who didn't. To order one of these washable wonders, send $42.45 -- or $31 for a carseat cover -- to Lambskin Inc., 1707 Third Ave. N., Seattle, Wash. 98109.

The next few weeks will seem unreal, but take heart. A premie usually catches up to his age by the time he's 2. And then you'll have to catch up with him.

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