In MISS MANNERS' set, the equivalent of "Let's put on a play in the barn! is "Let's start a salon." The chances of these projects being followed through to become brilliant successes seem to be about the same.

A salon, as Miss Manners understood it from dear Germaine de Stael, whose house was such a joy to us all, is a regular gathering of compatible intellects. The people in whom these intelligences dwell needn't be entirely compatible. But they must have a common body of knowledge and be able to use it with imagination and daring.

Miss Manners does not wish to denigrate the activities practiced at ordinary social gatherings. Eating, drinking, gossiping, flirting and showing off are the staples of human intercourse, without which there would be little incentive to stir from one's own hearth from one season to the next.

Nor does she suggest that these pleasantires be excluded from the well-run salon. But even food, much less sex, is not enough to keep the same people interested in encountering one another week after week in somebody's drawing room.

What is wanted is thought. Ideas that can be flirted with masticated, gulped to giddiness, and batted about are the only fit attractions for a salon. g

That is why Miss Manners has come to despair of the salon's being revived in modern times. We live in an era when people want only what they expect.

Intellectual stimulation to most, means hearing themselves deliver lectures on matters they have already figured out in their satisfaction. Arguing is considered to be exchange of thought. People keep citing their own experience and feelings, not because they have fresh first-hand material to offer, but from lack of one source of knowledge. Education and professional skills are so specialized that we have no common body of reference, and can only exchange trade gossip with immediate colleagues. Social trunover is required because we keep repeating ourselves, rather than continuing to develop our ideas.

All this leaves us with nothing but small talk. A salon requires big talk.

You can see that Miss Manners is rather pessimistic, and being already blessed with the staples of life that people seek at parties, disinclined to venture forth much. She has heard of gatherings at which everyone agrees in advance to read the same book and to limit conversation to discussing it, but this seems to her a paltry substitute for the free exchange of ideas.

It is, however, a start toward amassing and using knowledge for pleasure, rather than for personal or professional advancement. We could all benefit, in her opinion, from shifting our attention from our own feelings, to other people's thoughts.

In the meantime, Miss Manners is going down to the barn to see what's playing.

Miss MANNERS RESPONDS Q. I would like to share with you some comments made to my tall and lovely 13-year-old daughter -- comments made by well-bred, usually courteous adults:

Good grief! You're so TALL for your age!

I can't believe how TALL you are!

You've grown so much since I saw you three weeks ago!

How on earth does your family keep you in clothes?

Never do these adults consider their negative remarks about another's physical appearance to be the least bit rude. But how would these same individuals like to hear some of the following remarks about their physical appearance.

What's left of your hair is getting so gray!

You've gained so much weight since I saw you three weeks ago!

Why are your teeth so brown?

My, but you're flabby for your age!

Do you dye your hair?

what large feet you have!

Why are your teeth so crooked?

Several facts need to be faced.

1. Kids are getting taller and healthier and more physically fit than previous generations. Thank goodness!

2. One's size is determined at the time of conception. There is, therefore, little that one can do about height.

3. Continually hearing negative utterances about one's height can only make a child feel that there is something very wrong, in spite of parental assurances that tall is beautiful and normal. The end result will be self-consciousness, shyness, poor posture and a negative self-concept. Please, if you've ever made -- negative remarks about a child's size -- think about it. Say something positive to the child or buzz off!

A. Indeed. Miss Manners hopes you will not for a moment accuse her of arguing with your principle -- that personal remarks addressed to individuals of any age should be complimentary -- if she quibbles with your examples.

The expressions of surprise that children grow taller, rather than smaller, are not stunning instances of observation and tact. But Miss Manners does not see them as insults, either. It is generally agreed upon in this society that it is an excellent thing to age from birth to, say 30, but a terrible misfortune to exhibit any changes indicating one is continuing one's natural development from then on. Miss Manners has never understood why this is. To watch individuals change with the years can be interesting, if predictable, but to regard it as either a miracle or a shame seems naive and futile.

However, that is society's attitude, and Miss Manners is normally given to accepting conventions rather than fighting them; given this assumption, comments on your daughter's growth should be taken as compliments. Miss Manners suspects you see in them an attitude that she hopes and believes has been discarded by society -- that boys, but not girls, should be tall. Without arguing genetics with you, she endorses your policy of conveying a positive attitude to your daughter, and suggests that you extend this by teaching her to reply properly. Not, "and I see you're getting to be a little stooped over as you get older," but "why, thank you very much."