Q. My two daughters, ages 10 and 5, were watching a videotape at home in which adults were hilariously enjoying a joint. I immediately made my daughters turn it off, and we had a long discussion about the film: what was enjoyable about it (the silly humor) and what was negative (the poor values). I explained how the values of the film negated those of our family, and how the values of others may differ from our own.

I believe indoctrination about this horror can't start too young, but all the excellent documentaries about this national tragedy are on TV too late for my children to see. I'm afraid I may have overreacted because of my extreme aversion to drugs, as you can see by my use of "horror" and "national tragedy." I did stress in our discussion that the children always could talk to their father and me, no matter what they do. I'm not sure they believed me, since unfortunately, I did most of the talking.

I realize my control over my 10-year-old is short-lived; already peer pressure is strongly evident. I know, too, that parents must sow the seeds early and hope for the best. But teen-agers, of course, will experiment and go with the flow.

How do we sow these seeds without sounding preachy, stuffy, overreacting and unapproachable?

A. There is nothing wrong with calling drugs a horror and a national tragedy. They are and it is.

Your reaction may not be chic or trendy or cool, but it is responsible, and that's what a parent has to be. Drug use should not be a negotiable point for a teen-ager, whatever the flow. There may be experiments, but they don't seem so obligatory any more. More and more teen-agers are catching on to the dangers.

It's harder to predict who the burn-outs will be. The effects of the drugs are varied and so are the children who use them.

Some of the best-reared children--and some of the worst--use drugs, and an awful lot in between. Much will depend on your values now--and your supervision later.

Your control over your child isn't as short-lived as you think. Even though you must let go a little more every day, you're running the show so long as your child is your dependent. However, it takes more than a parent with an authoritative manner and the best of hopes.

Two-way discussions about drugs now are important and the more factual you can be, the more your 10-year-old will believe them. Television documentaries are good springboards for this--even if she has to stay up late. You can initiate others when you talk with compassion about some older teen-ager in the neighborhood who is mucking up his life. You don't have to give grave threats when there are examples around.

You'll be much more likely to keep your child from drugs if you give her an allowance too small to buy them, and, when she starts earning money at 13 or 14, you make sure most of it is spent in accountable, productive ways--like clothes or classes--or is put into a savings account for college (an account in which you or your husband is also a trustee).

Because a child usually tries drugs if her best friend does, you should watch her friends with more care from now on. If they change from being energetic, reasonably polite, delightfully unpredictable to listless, secretive, defiant, your child may have to change friends, for drugs may have caused these changes. She not only is too young to use drugs, she's too young to be a social worker.

And then there is the matter of permissions.

Your daughter will be out of step with the drug culture if she can't go out on school nights, and is kept busy with responsibilities, classes and activities after school and especially during the summer, when drug use often starts or accelerates. She also doesn't need to hang around the mall, or go to rock concerts--including the ones at neighborhood parks--or even Beach Week. The family can have other plans.

Contrary to prevailing opinions, a teen-ager needs a good deal of supervision until she's a junior or senior in high school and her conscience says "no" more automatically than it ever has before.

When you're strict on a few big issues, you can afford to be relaxed on a thousand small ones.