It is nonsense to think that only your best friend will tell you that you are obviously -- desperately -- in need of psychotherapy, a redesign job on your body, a new wardrobe to disguise your body, and a stronger bath soap.

Any strangers on the street will gladly tell you all these things and more. You can hardly stop them.

The more delicate of these free-lance critics flood Miss Manners' mailbox with requests for "tactful ways" to tell people how objectionable they are. Others believe in bluntness, on the theory that the message is so important that emergency delivery -- as when one yells "Fire!" -- is justified.

Even those on the receiving end are timid about questioning whether there is a need at all for everyone to go about telling everyone else how to live. Miss Manners is beginning to think that if more people stopped working on improving themselves and their neighbors, and devoted those efforts to improving the society, the world would go around a lot faster.

Meanwhile, the need for that best friend you can trust is greater than ever. It is just that the service such a person can provide has changed. Your best friend still tells you things for your own good, but they are things you will not hear from those who are devoted to improving you, rather than devoted to you.

Only your best friend will tell you that your party was a tremendous success, that everybody had a marvelous time, that the people who were screaming at each other were having a stimulating discussion, and the reason it broke up so early was probably that everyone had to get to early services Sunday morning.

The person who explains that you should have planned your guest list better, and that the reason so much meat was left over was that it had been cooked senseless, is not your best friend.

Nor is the person who says you should stick to clothing that emphasizes vertical lines, and not go swimming when anybody is looking until you have put in two or three years at a health club.

Your best friend is the one who shrugs when you moan about your physical condition and says, "Well, all I can say is it certainly doesn't show."

According to your best friend, your baby is perfectly beautiful. Your best friend therefore sees no need to inform you of corrective procedures available if the child still looks like that when he reaches adolescence.

Nor does your best friend tell you the monetary and sentimental value of the item you accidentally broke. Your best friend keeps a straight, indeed friendly, face as he or she assures you that it was of no importance, or confides that he never liked the silly thing anyway. If he accepts the compensation you offer, he agrees to do so only because that way you will be able to forget the incident as thoroughly as he has.

The person who sees both sides when you confess how a parent or in-law is driving you crazy, and suggests how you can stage a showdown with that person, is not your best friend. The best friend is the one who agrees how exasperating it is but manages to persuade you that it is bearable because it is also funny.

If the problem is with a child, the best friend does not trace it to your child-rearing methods; he tells you that the difficulty is a normal stage, which will pass.

Your best friend assures you that nobody noticed last night that you had too much to drink. Rather than inquire whether you have a problem, he volunteers that the problem was that dinner was served too late, and that frankly, nobody was in a position to look critically at anyone else.

A best friend never admits to having heard one of your stories before. If you realize in midsentence that he has, he says he had forgotten, or that it is his favorite and he wants to hear it again.

Nor does he admit having told your secret. Human nature being what it is, he probably did, but at least he saves you the anguish of remorse for not having been able to keep your own secret yourself.

Does all this mean that you have a liar for a best friend? Someone who will not take the same interest in helping you that the merest acquaintances are willing to provide?

Not exactly. It means that your best friend is someone who likes you the way you are, notices your strong points rather than your weak ones, thinks reassurance is a greater gift than criticism, and does not pretend to be in possession of a formula for perfection of which you badly need to be made aware.

If you have such a friend, Miss Manners begs you not to try to improve him. Cherish him.Q Twenty-one years ago, I gave birth to a daughter. I was not married and placed the child for adoption.

I have gathered my courage to search for my child and have good prospects of locating her. If I succeed, and both she and her adoptive parents are willing, I would like to acknowledge her as my birth daughter to friends and some family members who are completely unaware of her existence. Please advise me on this perplexing and delicate matter. A There are no forms for announcing the birth of an adult, and if there were, your daughter would probably object to your filling in the birth weight. And what would she do with the silver rattles sent by careless readers?

Miss Manners' point is that this is not a standard, conventional occasion requiring so little explanation that there is a standard way to announce it. It is something odd and special, which should be shared with friends whose sympathetic interest you can count on. Write them letters.

If, in the course of time, you become close with your daughter, and she and her parents would find it agreeable, you could give a party for the purpose of introducing her to your friends. Miss Manners hopes she need not tell you that the social emphasis should not be on her illegitimacy and rediscovery, but on your desire to have your grown-up daughter know your circle.