Q: A I am a 30-year-old working mother of a 3-year-old.

My husband and I always felt our family would be complete with two children. Now we aren't sure. Things are so much easier since our daughter is older and our lives are on an even keel. I also would have to keep working, and I know how hard that is with only one.

And yet I've recently been yearning for a baby. It is a feeling that comes and goes but I don't remember any uncertainty with our first child.

I feel time is running out. Even now there would be at least a 4-year difference in age, which I feel is too much.

I don't want to be sorry 2-3 years from now when it's too late, but I also want to feel we're doing the right thing at the right time.

A: Since you've thought of all the reasons why you shouldn't have another baby, it's time to look at the reasons why you should. Only when you examine every angle will you be able to follow your own instincts with surety.

The decision to have -- or not have -- another child is one of the biggest you'll ever make. No wonder the yearnings come and go.

Every woman who enjoys children gets these urges occasionally. Time is passing for you, but it isn't running out.

It's true that there would be a gap of four years or more between your children, but you can find arguments for and against any particular spacing. If the children are too close, there will be too much rivalry; if they're too far apart, they may not become good friends.

According to Joan Solomon Weiss, author of Your Second Child (Summit, $7.95), one expert thinks children should be less than two years apart; others think three years is best and still others say a 4- or even a 5-year difference between children is dandy.

In fact, no distance between children is quite right and none is really wrong. Children can like and enjoy each other even if they don't share the same toys, as so many remarried parents find out when they have their second families.

Much of your hesitation comes from having both too little experience and too much. Now you know the added burdens and anxieties that each child brings and yet you yearn for another because you know the joy that comes, too.

Your mind is telling you to be sensible while your body and your heart seem to say, "Go right ahead." Some sensible decisions are only sensible on the surface while others are right for one couple and not for another.

An only child is the only answer for some parents and they are rather sure about it although one or the other may yearn occasionally for another child. If this is just a passing fancy, it will occur with less and less frequency. The greatest problem for them will be the guilt they might feel if thoughtless friends or relatives urge them to have another child.

If you truly want to have a baby, the yearnings you have now will probably get stronger and last longer as the years go by. By carefully examining the pros and cons, you'll know if you can withstand the pressure later.

When you were pregnant the last time, you probably found the knowledge awesome, but in your heart you knew everything would be practically perfect. The baby would cry (but not much) and she'd need to have her diapers changed but she wouldn't have colic or take three years to get trained (ho, ho) and you never even thought about the germs she would catch or the sitters who wouldn't show up.

And then your child was born, introducing you to the realities and confusing your life more than you ever thought possible. She was (and is) so adorable, however, that you accepted them all -- just as you'd do if you had another baby. It's hard to believe, but a second child would be just as endearing and make you just as accepting as the first.

You would always have to juggle two schedules and cope with two distinct personalities, but many things that bothered you the first time would seem easy.

A second child not only makes parents feel joyful and excited, but efficient and competent. Bedtime, toilet training, discipline, mealtimes -- even getting out of the house with a diaper bag and a stroller -- will be much easier than it was three years ago.

It's the sense of joy and adventure that makes second (and third and fourth) children so rewarding, however. Every time parents weave another personality into their family, it becomes richer and more vibrant. There's also a hidden dividend. A second child can be a happy diversion when your older child turns 8 and the routines of parenthood and marriage become just a little boring.

The most persuasive argument of all, however, may be found in The Amazing Newborn by Dr. Marshall H. Klaus and Phyllis H. Klaus (Addison-Wesley, $10.95). Klaus, who put bonding in the parent-child lexicon, scientifically documents the way newborns see, hear, taste, smell and feel in an extraordinarily appealing collection of more than 125 pictures of babies less than 10 days old as they react to the adults around them.

If your yearnings can resist this book, you'll be blessedly happy with an only child.