Q: We have a bright, sociable 3 1/2-year-old son who has very few problems. His imagination and language skills permit him to have fairly lengthy (five-minute) conversations between two "toy people" or to discuss something with his baby sitter, his parents or his friends for five to 10 minutes at a time. His very favorite activity when playing outside is to chase around with another boy or girl or a small group of children.

My major concern at this time is his seeming lack of assertiveness. When another child directs his play, he invariably does what he is told. Unless he is provoked to anger, he adjusts his play to follow the demands of a more dominant child. The only times I have seen him direct the play is during a game of chase or during general roughhousing. The times that he plays as follower are frequently times when another child has "rules" for a game that our son has not played before (pretending to be at a hospital, for instance) or when the other child has the advantage of previous experience.

I'd like to know whether I am being overly concerned at my child's apparent lack of "leadership" qualities at this young age. I would like to encourage his development of leadership skills. Are there any books to help me?

A: It's time for you to learn every parent's hardest lesson: A child is his own person.

You and your husband created this boy and you care for him, love him hugely and give him many good times. Day by day you teach him the intellectual, social and moral lessons that will shape his character and his skills and give him the approval he needs to be self-confident.

That's all you can do or have the right to do. His temperament is entirely his own.

If a child is made to change his innate style, whether it tends to be aggressive, passive or isolated, he'll undermine his own integrity, as Karen Horney described so well in Our Inner Conflicts (Norton; $3.95).

Your son needs you to let him be himself, just as you've always done. It has worked well so far.

His temperament lets him give the lead to other children often, not because he's cowed, but because he's already mature enough to have sorted out the things that matter in his young world and those that don't.

He leads when it's important to him and gives the lead to others if they're more knowledgeable (or less deliberate) than he is. And he does this because he knows the job is more important than the glory it brings. That's a good, healthy attitude.

Although it worries you that he lets another child tell him what to do, he also shows you that he can take a high-spirited lead -- when he plays outdoors -- and he can get angry enough to say no. The rest of the time your son is what the world needs: a good team player.

It's hard to imagine a better way to make friends and keep them. His easygoing, outgoing personality is a harbinger of the good things to come.

The 3-year-old who tends to look before leaping will be the 8-year-old who'll stay off the frozen pond until the ice is tested and the teen-ager who'll let his buddy do the driving, but not if the buddy has been drinking.

He'll be able to be in a school play without grabbing for attention when someone else is saying his lines and be on a team or in a band without making a grandstand play.

Painters and authors and tycoons may succeed on their own, but most achievements depend on a group effort. It takes the contribution of many people to make a movie or produce a daily newspaper and if the operation is well-directed, every one of them will have a sense of satisfaction that comes from doing work and for doing it in synchrony with others. Joint effort brings a special joy.

The leaders of this century, like Gen. George Marshall, President Harry Truman and Pope John XXIII didn't come across as dynamic, take-charge people, but all of them were strong leaders.

Your child may never run the student council or even run his own business, but then, most people don't. If, however, he should find himself in a leadership role, he will learn what all successful leaders instinctively know: that he may be in charge, but he is still part of a team. He will have to do at least as much giving and taking as he ever did when he was just a player. His amiable personality will only make this easier.

To learn how 3-year-olds each play in their own distinctive, creative way, have your bookstore order Mollie Is Three, by Vivian Gussin Paley (U. of Chicago; $12.50). It's an eye-opener and a joyful one. In this nursery-school setting, you'll see that each child is different -- and wonderful. Just like your little boy.

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

Worth Noting

Parents can make reading a part of a child's life with the help of three fine new booklets -- for pre-readers, nonreaders and teen-agers published by Reading Is Fundamental. Send 50 cents per booklet to RIF, Box 23444, Washington, D.C. 20026.