Q. "We have three children -- Karen, who is 12; Jerry, who is 14; and Bobby, who is 16," writes a Rockville mother, "and every one of them driving me nuts.

"It's not that they are bad kids, you understand. They don't drink or smoke marijuana (I don't think) and they do pretty well in school and in sports, but they have such terrible manners at home.

"I don't care if they know which fork to use -- I only have one kind anyway -- or even if they eat with their fingers, although they usually, don't, but they are so sullen and rude to each other and to my husband and me. No matter what you tell them to do, it's a battle.

"If I had known what children were like 17 years ago, believe me, I wouldn't be a parent right now. But I am, so I'd like to know how to live through it."

A. One of the grandest dames we know once confided, "My dear, there are times in a marriage when only sex and good manners hold it together; but with children, there's only good manners."

You're going through one of these times.

You and your husband will live through it, of course, but the living will be more pleasant and the relationships tighter when some changes are made -- by everyone.

A teen-ager won't be rude very often unless his self-esteem is very low, or unless his parents ask for it. You do it two ways -- either by being such forelock-tugging patsies the child must push and push to get some limits, or by forgetting that the child deserves at least as much courtesy as the mailman.

Most of us fall into that second category.

Parents have such an enormous amount of power; it's hard not to abuse it. The pattern usually begins when the child is Mid-One and it is suddenly clear: This small person who has been running the house for 18 months is now able to take orders. What begins as "Please put this toy in the toy box for Daddy" escalates to "Put your toys away this instant" at Four, and by Seven every request is a command, without a please or a thank-you. It c an be the start of a sorry lifetime habit.

Although parents still expect -- and require -- courtesy from a child, they forget that manners are a two-way street. A teenager surely won't be polite to anyone who isn't polite too, including Mom and Dad.

At this point it's important to start over, even though you have to eat a deep dish of humble pie. This is hard to do, but take heart: There's no sight a child enjoys more.

Begin with a gathering around the table, but with no food or television or papers to distract anyone. Now ask to hold hands and explain that you feel the family lacks harmony. Tell them that you think better manners would help and you would like to start by being more polite yourself. Then ask how the family thinks you should change. This won't be easy and you may want to pull your hands away when they dare to say what you think, but hang in there.

If you are gentle and if you accept responsibility for yourself, your husband and your children won't feel defensive, and they will try to be gentle too, although some of the things they say may surprise and even hurt you. No one else sees us in quite the same charitable light we see ourselves.

It's only when you open yourself this way that you have the right to ask others to act differently too. At this point the conference may end in disaster unless you go easy. Remember, you want to make changes, not score points. You don't have to say everything all at once.

Aside from the conferences -- and you'll need quite a few -- there are some guidelines for manners that seem to make any household work better, although it will take about six months.

Lower the noise level. Don't shout from room to room, because yelling creates tension. When your child calls you, just say where you are and nothing else, so your child will come to you. And go to your child when you need him, unless you're terribly busy. (Parents have some perks.)

Turn off the record player, radio or television uless someone is listening to them. Noise is stress.

Talk in a normal voice, even when you're mad, and don't answer anyone who yells at you until they lower the decibels.

expect good manners. You do this when you and your daughter reach a door and you just stand there. If you don't open it, she will, and then you slip through, fast as a flash, and thank her SO MUCH for opening the door for you as you hold it open for her.

Show respect. Ask for help, don't order it. And when you do ask, give an idea of the time the job will take and when it must be completed. A child's time is as serious to him as your time is to you.

Act glad to see your children when they walk in the house.

Ask your children what they think would be the best way to do a troublesome job, like marketing. They have been watching you muddle through for years and have a lot of ideas to make things easier. Try some.

Knock on their bedroom doors before you enter, and never, ever open or read their mail or go through their things.

Listen to your children individually and as thoughtfully as you would listen to your boss.

Manners are threaded through everything you do and it all comes down to kindness.