Exquisite manners are much more necessary when one travels steerage than they are in first class. If you don't believe Miss Manners about this, check it with an ancestor who immigrated under these conditions--or just hop onto a flight of more than six hours' duration and experience it yourself.

Miss Manners does not mean to trivialize the tremendous hardships suffered by so many citizens who, for hundreds of years, endured appalling voyages before they arrived in America. Traveling in what is now called tourist class, one does not generally run the risks of disease associated with steerage, nor do the trips last as long, although they certainly seem endless.

But on the smaller scale, one can easily imagine how difficult and essential it is to control one's behavior for the sake of all when one is thrown among strangers in a densely crowded, self-contained space with poor hygienic facilities and worse food.

In first class, breaches of good manners are, while deplorable, less likely to have widespread consequences. There is more room, less competition for basic services and, in theory at least, attendants available to smooth things over.

Back in steerage--er, uh, tourist--small infringements can easily have a wide effect on the well-being of many. Basic manners are therefore not enough; one must also be on the lookout for the general welfare.

This is an excellent argument against being sick on an airplane, or allowing one's children to be. Being sick is the classic case of something that, while not actually rude, causes great discomfort to others. Failing the ability to exercise such control, one should at least be neat about it.

Other helpful forms of behavior include:

Organizing one's hand baggage before boarding in such a way as to make it possible to slip into one's seat with it and then distribute it overhead and underfoot, rather than standing in the aisle doing so while several hundred people pile up behind you.

Taking no more than one's share of the amenities--pillows, blankets--and of storage space, and less of that, if possible.

Cooperating in exchanging seats with people who want to sit together, see the film if you don't and they can't from their assigned place, or be farther away or nearer to the smoking sections, if you don't care.

Spending as little time in the bathrooms as possible, for which Miss Manners will give special dispensation to do moderate grooming at one's seat.

Staying out of the aisles and out of the way of moving service carts.

Not begrudging moving to let those in one's row out when they deem it necessary for whatever reason.

Controlling one's children from such voluntary actions as kicking the backs of the seats in front of them and endowing them with strong constitituions so they do not indulge in involuntary unpleasant actions as referred to before.

Q: My sister-in-law-to-be is about to send out her wedding invitations. Can you please tell us if it is proper to send an invitation to all the bridesmaids and ushers? Or do you just assume they already know, so why waste an invitation?

A: "Never assume," Miss Manners' first editor used to snap at her when the girlish Miss Manners would try to reply timidly to factual questions with, "Well, I assume that . . ."

It was excellent advice. Miss Manners would advise against assuming the wedding party will remember the time and place without a written document stating them, and that they will be above pretending not to if you commit the rudeness of not "wasting" invitations on people to whom this courtesty is due.

Q: My grandmother has an invariable response to the problem of dealing with people who call up on the telephone and then demand, "Who is this?"

She responds, "I have no idea." Her tone is courteous, but if the ensuing silence lasts more than two or three seconds, she hangs up.

Don't you think she should allow a little more time for the caller to make a fresh start?

A: Perhaps. But Miss Manners has fallen so completely under the charm of your grandmother, just from your brief description of her, that she wouldn't attempt to change the least little thing about her for anything in the world.

Q: Am I correct to assume that it is always impolite to invite oneself to another person's home, even if one is a child?

This problem arises with some of our younger neighbors, who phone to ask, "Can I come over to play with Beauregard?" A variation occurs when one of my children invites a same-age friend to play, and minutes later, both that friend and his or her sibling appear at the door.

I can only assume that the parents encourage these calls and uninvited visits, since these same people have come to our door with a child in tow and announced cheerfully, "Our Matilda would love to play with your Beauregard."

I do want my children to play with their neighborhood friends, and I do invite those children to play in our home when it is convenient for me.

Also, should one accept an invitation if one has no intention of reciprocating? Some children who have visited us more than once have never invited my children to their homes. (In case you're wondering, other parents and teachers have informed me that my children are well-behaved.) My feelings are hurt when my children are not invited back, but fortunately my children do not seem to mind very much.

In summary, how do I set an example of good manners for my children, protect myself from nervy parents and protect the friendships and feelings of all the children involved in these matters?

A: By all means, teach Beauregard to reciprocate invitations, and to refrain from issuing himself invitations to other people's houses.

Then all you will have to do is to teach him the higher forms of etiquette, which include refraining from critiquing the manners of one's playmates and conducting one's social life without keeping strict tabs on what other people are doing for you.

The fact is that the social life of small children is conducted with less rigor than that of adults. Whose yard or house is played in more often is likely to be a matter of whim or convenience, and having children trailing through one's house is not in the same category with full-fledged entertainment of adults. You do not need to dress up for these visits, or sit around and make conversation.

You don't even need to have them when they are an annoyance. If a child or parent proposes such a visit, there is no reason that you cannot reply, "Oh, I'm sorry, this is not a good time." The same may be applied to drop-in adults, for that matter.

Miss Manners certainly encourages you in teaching a higher standard to your children than the prevailing neighborhood one. She hopes she has given you more time in which to do so by freeing you from the obligation of bringing up the neighborhood children and their parents.

Q: Would it be considered improper for a man who is engaged to be remarried to place a memorial ad in the local newspaper on the second anniversary of his wife's death?

A: No, one cannot exactly consider this improper. It is imprudent beyond belief, however. Why any gentleman would wish to be so provocative unless he is excessively fond of scenes or weary of his engagement, Miss Manners cannot imagine.

The departed do not, as far as we are able to ascertain, keep up with the newspapers. One therefore has to assume that the intended readership for such a notice consists of the gentleman's acquaintances, all of whom are also acquainted with the fact of his engagement. They are bound to think less about his late wife's reaction to this than of his present fiance''s.

The gentleman will discover that you need not be improper to get into serious trouble.

Copyright (c) 1983, United Feature Syndicate Inc.