SUPPOSE THE postman arrived during breakfast (more likely dinner, at his rate) and insisted that you leave the table and read your mail immediately. No matter whether a letter consisted of advertising, a leisurely chat from a friend or relation or business matter, it had to be attended to that very minute.

If you happened instead to be entertaining guests, doing business, taking a bath, listening to a symphony, making love or any combination of these activities, you would still have to stop everything immediately and devote your full attention to anybody who chose to address you.

This is what most people allow the telephone to do. It has developed into a horrid instrument, always clamoring for attention, and Miss Manners is beginning to think that it ought to be abolished entirely, as it never seems to learn to behave itself.

There's the whiney bell. Like a spoiled child, it figures that people will give it whatever it wants just to shut it up. And, like weak parents, nearly everybody does.

Now, Miss Manners always has sympathy for people who complain that they are treated rudely by the people whom they telephone. Always, that is, except when they call to say this just when Miss Manners is in the middle of doing something interesting. Miss Manners is always doing something interesting, such as looking out the window at the trees.

Such people should not be put on hold indefintely, made to spell their name more than once, told that person they want is out after they have been asked for their personal histories, hung up on or subjected to canned music.

However, these people would spare themselves the possibility of many such insults if they would make fewer telephone calls.

Telephoning is not the only way to do business. It is not even always the quickest way of doing business. Two people who keep different office hours, either from the nature of their jobs or because they live in different time zones, may easily spend days leaving messages for each other -- even more days than it takes to send a letter.

Social matters, too, are automatically put on the telephone when they may be better handled by mail. A whispered long-distance "I love you" is sweet, but a written one keeps forever and may be produced later in court.

The telephone is used, not only out of a bad national habit, but because a quick answer is wanted. This overlooks the likelihood that the quick answer may then be regretted, and a second call is necessary, to reverse what one has said. ("I'm so sorry, Calvin tells me he forgot to mention that he had already promised we'd go slumming that night with someone else.")

But it will only be possible to use the mails, with their better manners, if we all promise to answer our letters promptly. The telephone can be reserved for truly urgent matters then, and there can be a stop to that incessant ringing in Miss Manners' ear.

And please don't say you have no time to write letters. You will have all those wonderful hours that you used to spend on hold. MISS MANNERS RESPONDS

Q: Here's an entry for the Silliest Argument of the Year Award. Last night, my wife and I were about to go out when I noticed a black speck in the corner of her eye. I reached over and wiped it out. She pulled back as if I were going to hit her, and in the process I got my finger in her eye. She claims that she didn't know what I was going to do and was afraid I would spoil her make-up. Never having beaten her up in my life, I claim that she was crazy to assume I would harm her and that anyway, it was an affectionate gesture, and if she really loved me she would care more about that than her make-up. What do you think?

A: That no good can ever come of a sentiment that begins "If she reallyy loved me she would . . . " Perhaps if you tried, you could find another gesture that expresses affection without affecting the decor.

Q: What do you do if a waitress tells you it's not "restaurant policy" to issue separate checks to two couples dining together?

A: Separate yourself from the restaurant before ordering dinner. If there are enough crumpled napkins left behind by people who depart from the restaurant when this is announced, there will be a change of policy.

Q: I am feeling very incorrect because I do not have black or blue-black ink, or white paper. I have only green ink. Please, tell me, what I can do?

A: Save up all your letters all year long, and answer them at Christmastime.

Q: Pamela and I have been best friends all our lives, and always will be. Hopefully. We survived a lot of squabbles when we were little kids, living two blocks from each other, and a big problem when she left college, where we shared a room, to marry a boy I didn't then like. Now he's a best friend of mine, too, and was the main one who helped me two years ago, when my father died. One problem I had at their house has now been solved -- they always used to be urging me to get married, and if I brought a boy friend there, they would go into this newlywed happiness act, holding hands, etc., to give the boy the idea, and I had to stop taking anyone there who might scare easily.

I say that's solved now, because I am getting married, and there's no reason that the four of us can't be best friends, as my fiance likes them very much. That is, there is only one reason, similar to the problem I had before.

Pamela and Richie have a four-month-old baby. We have great times when they get a babysitter and we all go out together, but that's all there is to the friendship any more. If I go over to the house during the day, Pamela is always too busy to talk to me. Even if the baby is asleep, she's running around doing things for her. For instance, she's going to be my matron of honor but she hever has time to talk about my wedding plans with me.

And if I go there in the evening, with or without my fiance, they make the baby the center of attention, and then they do a new act -- about how wonderful it is to be parents, and how we ought to have lots of babies. We're not even married yet, and anyway, I'm not sure I ever want to have children. Not if it dominates my life like it does theirs.

Are Pam and Richie always going to be one step ahead like that? Should we forget about them and find friends who share our interests now?

A: 1. Yes. 2. No.

Indeed, the great milestones of life, such as marriage and parenthood, are fascinating to those who are in them and less so to those who are not. It is interesting that Richie was of particular comfort to you during another, less attractive, such time; perhaps he had known what it was, before you did, to lose a parent, as he has known before you the joys of marriage and parenthood. This time difference will sometimes be an annoyance to you, and sometimes an advantage.

Are we to have only temporary friends whose experience happens, at the moment, to match ours? Miss Manners sometimes fears that we live in a society where friends, and even spouses, are supposed to be relevant, like college courses in the 1960s, or else discarded.

Her suggestion to you is to make a new friend -- of that baby. If you do have children of your own, you will find the experience useful, and if you don't, you may be especially grateful some day to have a friend in a generation younger than your own.

One should not wait to begin such a friendship when the child reaches whatever stage of development you now consider interesting. If you begin to enjoy that child now, either while the mother is there or, giving the mother a chance to get away, by yourself or just with you and your friend, you will enrich your friendship with her parents and probably develop a new lifelong friend.

Q: My mother-in-law has awful table manners. Not only does she not use serving forks, but she eats with her fingers, saying the food tastes better, and spits out the "skins" or anything she feels is too tough in a half-chewed wad on her plate. We are going to visit her soon. Is there some polite way to tell her how unpleasant this is? She does not take criticism at all well.

A: In the annals of etiquette crimes, correcting one's elders and correcting others in their own houses are more heinous than regurgitating food onto one's plate. Miss Manners suggests you direct your critical feelings towards your children's table manners. Children have no choice about taking criticism. If it will enliven your visit, you may correct them for doing the same thing their grandmother is doing, at their grandmother's table.

Q: One might think that an intelligent, well-educated, single lady in her late 20s would not want for invitations to dinner parties -- unless, of course, one is such a lady, in which case one knows better. The average hostess, it seems, considers unescorted female guests as inadvisable at her dinner table as canned vichyssoise. Please, Miss Manners, encourage your readers to include their single friends when they entertain.

A: Miss Manners is afraid that the average hostess thinks that her single friends will only be amused at her dinner parties if she provides them with potential sexual partners, and that they are unlikely to give their fair share of return dinner parties. This is a most unfortunate state of affairs. Miss Manners will urge married hostesses to include single people at their parties, whether or not they are exactly matched up with other single people, if you will promise to invite married couples to such parties.

Q: Is it proper for a woman to get married in white the second time around.

A: Many people think that a white wedding dress is the packaging for an unused bride, which gives them a good snicker at most weddings. This is not true, however, that it is conventionally associated with a first wedding. Wearing off-white, which is practically the same thing, for a second wedding may prevent the snickers of those who believe in the sanctity of this rule. Then again, it may not. People always seem to be snickering at weddings these days over one thing or another.

Q: What is the correct salutation for a business letter when one is unsure of the sex of the person involved? "Dear Sir" and "Gentlemen" are obviously impractical, but I find no workable alternative. In today's world, the head of a department could just as easily be a woman, and I dislike the possibility of offending her.

A: In today's world, when most companies address individuals as "Dear customer," "Occupant" or "To Whom It May Concern," Miss Manners is touched to know that the recipients of these letters visualize a human being opening their replies and that they care enough to speculate on that person's gender. She is ashamed to have nothing more human to suggest than "Dear Madam or Sir" or "To the Credit Department Manager." But, then, the business world has always been a cold and cruel place.

Q: When is a VASE a VAHSS?

A: When it is filled with DAHSIES.