ON THE subject of manners for children, many adults believe that the opposite of "polite" is "creative." Poor little mannerly children, they think -- how suppressed and inhibited they must be.

Actually, the opposite of "polite" is "rude." And if you think that rude children are better off emotionally than well-behaved ones, you are in luck, because there are so many of them around. What an increasingly joyful world it is getting to be as they all grow up and take charge.

Miss Manners, as you may guess, believes in manners for children. As a small lady in her jurisdiction replied, when asked in pitying tones if she were expected to be polite all the time, "You bet your Aunt Fanny I am."

Miss Manners has also observed that when children are truly allowed to express their preferences, uninfluenced by the dreary adult expectation that they must all be artistic and original little noble savages, they come out resoundingly in favor of rigid traditionalism. The devotion to ritual exhibited by your average toddler in regard to his bedtime routine would make a 19th-century English butler look like a free spirit.

There is an instinctive acceptance of the idea of right behavior and wrong behavior, even if the child cannot, or does not care to, sort the human possibilities into the proper categories. There is hardly anyone more forlorn than a child who, on being thrust into a new social situation, is instructed to do "whatever makes you feel comfortable."

The fright of a basically decent child on finding himself on a solo visit to a friend's house, without having been warned what the common standards are in the way of pleasantries to adult hosts and table manners, is exceeded only by the terror of a pubescent child anxious to appear as if he knows what he is doing, or should be doing, at his first boy-girl party.

By the time the pitiful child who has been subjected to manners instruction since birth gets to this point, polite behavior has become second nature, and he is free to enjoy himself without fear of inadvertently doing wrong.

A good parent owes it to a child to teach manners as an interesting and useful skill, and not a subject that is invoked to characterize whatever the child happens to be doing when the adult is feeling irritable.

It does mean that during the training period (birth to marriage), the entire household will have to conform to the practice of exchanging greetings and simple conversation; a pattern of consuming food in ways that are esthetically and socially presentable; civilized restraints upon anger that allow it to be expressed without throwing out all respect; a pretense that one is interested in the comforts and adventures of others; and the principle that guests, regardless of age or personal charms, deserve to be treated hospitably.

Once a parent learns to live this way, he will find it not unpleasant. And for the child, such standards are so much less strict, rigid, cruel, inhibiting and pitiless than peer pressure standards, which are always quick to fill any vacancy left by lackadaisical adults. MISS MANNERS RESPONDS

Q. My friend and I recently had a disagreement about how a lady should sit. She claims that crossing your legs is unladylike, but when I inquired why, she did not give me a reason.

I remember reading once that a lady may cross her legs at the ankle or knee, but not at the calf, which causes an unsightly bulge. What is the rule of etiquette on this subject?

A. What is the lady sitting on? If it is a horse, for example, the reason she should not cross her legs is that she will fall off.

You see, much as Miss Manners loves beginning her statements with "a lady always . . ." she recognizes that occasionally even a perfect lady must consider the circumstances. In sitting questions (as opposed to standing questions) her clothes have much to do with the answer.

A lady wearing a miniskirt properly sits with her legs pressed tightly together at the thighs, knees, calves and ankles. (She may splay her toes to relax, if no one is looking.)

A lady in a respectable skirt need not be quite so rigid, but may sit with her ankles crossed (the preferred sitting position for ladies), legs parallel but uncrossed (this holds second place), or even one leg crossed over the other (considered rather racy by strict standards). In all of these positions, the knees must meet.

A lady wearing trousers may certainly cross her legs, and if her clothes reek of activity, so to speak --if she is wearing jodhpurs or a dance leotard with tights or ski clothes--she may even rest the right ankle on the left knee, generally considered a posture for gentlemen.

A lady in evening clothes must keep her knees and ankles together--unless, of course, she is playing the cello.

Q. I am wondering what times of day are and are not appropriate for paying a call or telephoning, assuming there is no emergency.

Two weeks ago, we received a call at 11:30 at night from one of my husband's business associates, regarding a routine matter. We had been home all evening, and were falling off to sleep by that hour.

This morning at 7:15, the representative from the electric company banged on the door quite loudly and yelled, "MR. SMITH, MR. SMITH!" (not our real name) until we woke up and my husband got up and answered the door. My husband told him he didn't like being awakened, and the man's behavior indicated that he knew that he was doing exactly that. My husband told him to come back at a civilized hour and knock or ring the bell like a gentleman.

Was my husband out of line? How early is too early? How late is too late?

A. If you really want to know when Miss Manners thinks it inappropriate for people to call uninvited at one's house, in person or by telephone, more likely than not shouting a name that is not one's real name, it is: early, late, mealtime, naptime, the family hour, the reading hour, conversation time, quiet time, when one is housecleaning, when one is changing the baby, and when one is in the bathtub.

The only proper times, in other words, are when one is thinking how much housecleaning there is to be done, when one has decided to write a novel, or when one has just fallen in love and is not sure whether it is requited, in which case no time is inappropriate.

In the absence of servants who announce blandly that no one is at home, and for those of us who cannot warm up to answering machines, the answer is the mail.

That is not, however, the answer to any question you have asked, is it? Treat it simply as a warning that there are crankier people even than your husband in the world, and that callers should therefore either deliver urgent messages quickly ("I live across the street and I wondered if you know that there are flames coming out of your attic") or inquire timidly whether they are intruding ("Is this a good time to discuss the habits of your dog?").

Basic weekday calling hours are 9 in the morning to 9 at night, with particular caution exercised between 6 and 8 if one is not sure of the dinner hour of the callee. Efforts should be made to ascertain the habits of those on whom you wish to intrude.

People known to have small children can be presumed to get the day under way earlier, although they do not take calls the hour before school starts, except announcements of the irrevocable breakdown of car-pooling arrangements. Anybody who works a night shift should not be called before noon, although it is more polite to take the trouble to find out what time he or she starts the day.

As to the question of handling intruders, no, your husband is not supposed to give early-morning etiquette lessons to the man from the electric company. It would only invite a lesson in counter-etiquette, which is to say a punch in the nose or the verbal equivalent; or a discussion of the hours, requirements and difficulties of reading meters for the electric company. Neither is conducive to sleep.

It is obviously in your interest to be as brief and unprovocative as possible. "I'm sorry, I can't talk now," or "I'm busy, I can't let you in now," followed by hanging up the telephone or shutting the door, is the easiest method, although not one whose effectiveness Miss Manners is prepared to guarantee.

She is very sorry that some people do have to do business in other people's homes, and has no doubt that their frustrations are legion. But they cannot expect the world to live in a permanent state of being on call.

Feeling incorrect? Address your etiquette questions (in black or blue-black ink on white writing paper) to Miss Manners, in care of this newspaper. Copyright (c) 1982, United Feature Syndicate Inc.