THE NEW mother proudly introduced her 14-year-old daughter, whom she and her husband had recently adopted. "Do you have any real children?" was the reply.

"What did she think this one was?" asked the mother in recounting the incident. "Polyester?"

There are perfectly good conventional statements to make on all of life's major occasions, and the appropriate one for this was "Congratulations," with perhaps some babbling on about the charm of the child and the good fortune of the parents.

It is when people start making up their own comments, reflecting their thoughts, sentiments and philosophy, that Miss Manners begins to worry. Nearly all of these are ill thought out and, if subject to the slightest scrutiny, crude and rude. So much for the natural impulses.

Anyone who has ever been subject, when bereaved, to the improvised consolation of people who refuse to let it go at "I'm so terribly sorry" will know what Miss Manners means.

Now, adoption is a happy occasion. But you would never know it from the usual comments it elicits.

Most people seem to assume that it is a last resort move to settle for an arrangement that was far from what was actually wanted; further, they assume that they should feel free to indicate this when talking to the parents and to, or in front of, the child.

Typical remarks, adoptive parents report, are:

"Couldn't you have any of your own?"

"Didn't his family want him?"

"Why didn't his family want him?"

"How can you be sure that there's nothing wrong with her?"

If there are children in the family who were not adopted, the question is, "Which ones are real?"

If the adoptive mother becomes pregnant, she is subjected to the popular belief that tenseness from wanting children had prevented her pregnancy until adoption got her mind off it. "See, it worked--you got pregnant" and "Well, you didn't have to adopt, after all--you're going to have your own" are the standard remarks in this instance.

If the child is adopted at an age old enough to have insults delivered directly, he or she is generally asked, "Why didn't your parents want you?" or "How come you had to be adopted?" or "Why weren't you adopted when you were little?" But subtle people prefer to address these questions to the parents while the child is standing there.

Miss Manners is running through all this nastiness that poses as social conversation among friends not only for the purpose of telling those who indulge in it to cut it out this minute, but also to remind adoptive parents of the importance of teaching their children not to answer rude questions simply because they were asked.

Actually, this is a social skill that all of us badly need in these nosy days, when "Can you tell us how you felt when you saw your family being killed?" is considered to produce a commodity oddly labeled "news."

Although Miss Manners is not ordinarily partial to the snappy comeback, she will not try to discourage those who teach their children to look the questioners straight in the eye and reply, "Why do you ask?"

For parents, however, she prefers something more sophisticated. How about a small laugh and the observation, "My, we had no idea how curious people are about where babies come from." MISS MANNERS RESPONDS

Q. I'm a 16-year-old male who enjoys going out to dinner as often as I can, but what I don't enjoy is those nosy old women who mumble to each other about how terrible someone else's manners are. Why can't they keep their comments to themselves?

I mean, I could understand if someone was bobbing his face in his plate, but not little things like clicking his fork or smacking his lips.

I think if someone pays hard-earned money for a nice dinner, he shouldn't have to listen to rude comments while he dines. I have something to say to all those elderly folks: "The bad manners are in the bad comments."

A. You are correct, of course, much as Miss Manners hates to side with you because of the uncharitable tone of your letter. The breach of manners by those who make audible comments about others is, indeed, worse than the manners that excited their comments.

On the other hand, you mention that these ladies are mumbling. Is it possible that you were straining to eavesdrop on others, an instance of bad manners that would be worse than whatever it is you heard?

Let's call this one a draw, shall we?

Q. A friend and I are standing in my kitchen chatting, and right across the light-colored counter facing my friend strolls a cockroach. What is the proper thing for me to do under the circumstances?

A. Say, "Oh, I don't feel like cooking, after all. Let me take you out instead." It may be expensive, but Miss Manners has the feeling that "Oh, there you are, Fido," wouldn't work.

Q. I want to have a wedding. The problem? I had just come out of a divorce four years ago when I started living with a guy, and now that we have a child, we want a proper wedding. But would it be proper?

Our families know the situation, but most of our friends think we are married.

I've known women in my situation, and they chose to go to a judge or not get married at all. I don't want to do that!

Would it be best to:

1. Go to a judge and be married, then have a wedding to reaffirm our vows? or

2. Go ahead and have a wedding of choice? or

3. Forget the whole thing?

Since this will be my second marriage, I want a simple wedding. Is there a proper way for this new beginning?

A. There are some cases, Miss Manners is forced to acknowledge, in which propriety is relative. Not getting married because to do so would seem improper is such a case: You are not going to get any more proper by waiting.

Ordinarily, Miss Manners would give you her standard lecture about the Snicker Factor at weddings. It is always there (if it is impossible for anyone to snicker that the couple has been living together, then some will snicker that "they hardly know each other"), and you simply have to decide how much of it will bother you, and whether it is worth doing what you want to anyway.

But here you have a child whose reputation your status affects, and he is so far protected from snickers by the general belief that his parents were married before his birth. Please do not sacrifice that for a party.

As a matter of fact, you do not have to sacrifice the party. You can even have the wedding itself in front of everyone, if you call it a reaffirmation of vows. And surely you must have made some promises to each other four years ago.

Q. I have been dating a man for four years, and I have a 6-year-old son. When "Mother" comes for a visit (every two years or so) we go out to dinner quite often.

Here's the problem: My child is well behaved in public, but as soon as the meal is served, "Mother" starts picking at my son to "hold your napkin like this--use a knife and fork to cut the drumstick" (he just learned to master a fork), "leave your milk on this side; your spoon stays on your plate," etc.

Needless to say, dinner is quite unpleasant, and my son is so frustrated that he often refuses to eat, hangs his head and pouts.

I have told "Mother" that I will take charge of my son when on outings, but she will not let go. He has manners and is not a slob. I plan to marry her son, so I want to stop this now.

A. Once you marry her son, will you have dinner with Mother more often? If not, Miss Manners is not going to take the time to prepare you for an event that will not occur until your child is of an age to eat properly.

But what you heavily suggest is that no one will ever eat properly enough for this lady, who does not seem willing to allow you the task of bringing up your child.

Why, since she will be the child's grandmother, don't you let her try? Leave the child with her, some time when you and your husband need a holiday, and suggest that they form a relationship. This is not so cruel to the child as it sounds, as no person in her right mind would spend all her time carping at a child who is old enough to show resentment and to tell tales. With temporary total responsibility, she is likely to temper her criticism with reason and perhaps affection, and it may turn out well for both of them.