Q: I am six weeks pregnant (an accident) with my third child. We have two wonderful kids -- a 7-year-old boy and a daughter, almost 5. They are both happy and well-adjusted and I love them completely and enjoy them immensely.

I feel ambivalent about the prospect of a new baby. On the positive side, I adore children and have always rather longed for another. I love being a mom and would no doubt enjoy the experience.

There are some problems, however.

A third child would mean the indefinite loss of my part-time income, which would mean a significant change in our life style. We were just getting to the point when we could have a few extras -- a short vacation, a new piece of furniture, an occasional night out. I realize this sounds materialistic, but it is comforting not to have serious financial worries.

This also blows a large hole in my career, which was just getting started. It is difficult enough to work with two children, but the thought of trying to put together the logistics for working with three children is terrifying.

Lastly, the gap between the first two and the baby would be significant. I liked having my first two together because they play with each other and relate well. I'm afraid the family dynamics would be thrown into a whirlwind.

I am considering terminating the pregnancy. My husband wants to keep the baby, although he will go along with my decision. However, I can't seem to get rid of the guilt feelings and am really on the fence. Older friends have always advised me not to worry about money. Most of my peers have only two children and feel that three really is one too many.

How can I come to a quick (and I hope not too painful) decision?

A: A decision that is logically right can be psychologically wrong -- and from the tone of your letter, abortion seems wrong for you.

Two lines in your letter tell you why: "My husband wants to keep the baby" and "I've always rather longed for another."

An abortion could cause a serious rift between you and your husband. Even after six weeks, you both already are bound to this unborn child.

Its loss also could cause unexpected, almost unquenchable grief for you. Over the years this column has received many letters from mothers who, even years later, still mourn the children they've aborted or miscarried or who were stillborn. Moreover, there is the grave moral issue. Abortion may sometimes be the more moral course for many people -- if the mother was raped, for instance, or if she or the family couldn't handle the emotional or physical impact of a baby -- but you can do it if you consider the same concerns from a positive point of view.

Ambivalence is a good example. You may have an extra dose of it, but most pregnant women feel ambivalent at one time or another. And after the birth, you'll find that the love you give the new baby, and the pleasure you get, will make you love and enjoy the older children even more. Never will motherhood seem so rewarding.

You also say that you'd lose out on your career for a while, but would this really happen?

You may have to get a housekeeper to stay at your house or cut back a few hours a week for a while, but it won't be impossible or as hard as you think.

Since you now manage a part-time job with two children, you should be able to manage it with three. Your friends with two children don't know the big secret: The third child practically turns a parent into an efficiency expert. You'll be amazed how much more you'll be able to do, and the ease with which you do it.

Some of your efficiency will come from the help you'll get in the family. The gap that seems so great will be a godsend next year.

Children traditionally like dolls in the middle years, but a baby is the best doll of all. With any encouragement, your son will do much of the feeding and rocking and reading and your little girl will often fetch diapers, pick up the baby's toys (but probably not her own) and push the infant swing for you if you include her in the baby-tending business and take the newborn to her kindergarten so she can show 'n' tell (and brag).

The baby probably won't even be as expensive as the first ones were. You already have the equipment and clothes; you know now that babies need much less than you once thought and you know how easy it is to borrow from friends or buy more at yard sales. Aside from well-baby checks, the costs of a third child go way down.

There will be changes: You will be more tired. You won't have as much money. You may join a baby-sitting co-op to go out at night and you may go camping for your vacations.

The baby will affect the family dynamics, but that's the magic of a family. It continues to grow and change, just like the people in it.

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

Worth Noting

Young musicians, 5 to 13, from D.C., Maryland and Virginia, can audition for the prestigious D.C. Youth orchestra at 9 a.m. Saturday. Bring your own instrument and music to Coolidge High School auditorium, 5th and Tuckerman, NW. For more information, 723-1612.