"PERSONS WITHOUT a sense of humor always write long letters," observed a dear Sir Herbert Beerbohm Tree, the great actor, "and I have noticed, too that all madmen write letters of more than four pages. I will not venture to asert that all persons who write more than four-paged letters are mad. Still, the symptoms should be watched."

As Miss Manners recalls, dear Sir Herbert was referring to dear George Bernard Shaw when he spoke of madmen without humor, but nevertheless it has always seemed to her an observation of remarkable truth. We are all quite mad and humorless upon occassion, and we all seize those occassions to fire off letters of four pages or more. The symptom should indeed be watched.

You know that Miss Manners is always encouraging, even begging, people to write letters. She spends much of her life urging you to write business letters instead of arranging oral duels between your secretary and somebody else's about who is going to get on the telephone when; to write charming little notes to bolster the generous impulses of those who have offered payments, hospitality and favors; to pen such simple sentiments as "congratulations" or "I love you" rather than waste time looking for commercial greeting cards to express them for you; and to conduct the interesting transactions of your life in such a way as to leave plenty of material for your biographer, perhaps even enough for a separate volume of letters, rather than to paper the would with telephone messages.

She recognizes, however, that there are some letters that ought never to be written. Most of them happen to be four-pages long.

All letters that begin, "Never in my life have I been subjected to such -- " all fit into the category of letters that ought not to have been written. So do all letters that begin, "You may not be aware of it, but I have feelings too." (Miss Manners would go so far as to say that all people announcing, "I'm a person,too," should be strictly avoided, at least until they have managed to pull themselves together.)

Letters explaining "God's feelings," how they happen to coincide with the letter-writer's, and what God plans to do to the receiver of the letter, should not be written. These carry double violations, as they are traditionally nine pages long and have extra writing up the margins of the lined yellow paper on which they are written.

Threats in general, name-calling and other insults are not worth writing, because their effect tends to be humorous, rather than frightening. Letters correcting the information and grammer of others should probably not be written, but at any rate should not be written in high sarcasm, because they are bound to contain errors of their own.

In is not a good idea to write letters that make clear the existence of a relationship that the receiver has not confided to other people of the same mailing address, such as her parents or his wife.

Miss Manners would be remiss if she did not pass on to you a suggestion about what to do if you find yourself seized with the desire to write one of these letters. She turns, again to dear Sir Robert, who said, "One of the most alarming signs of insanity, it has often seemed to me, is that of writing to newspapers (invariably more than four written pages) to prove that Hamlet was sad, and that Bacon wtote Shakkespeare . . . I am satisfied that many of the learned commentators have only been kept out of lunatic asylums by the energy which they expended in the harmless occupation of discussing these two kindred subjects in print.

"In many cases it has proved a most valuable safety-valve."

MISS MANNERS RESPONDS

Q. Many adolescents, not particularily known for their politeness, rudely declare, "It's not polite to point," when someone points a finger at them for emphasis. It seems to me that in this case, they learned only half the lesson. It is impolite for A, while speaking to B, to point to C. who is beyond the range of hearing but within the range of sight, and therefore doesn't know the reason for the pointing. But if A, while speaking to B, points a finger at B to stress a idea, such as "It's up to you!" or "The error was yours!" there is nothing impolite about such pointing. Am I correct?

A: Please remove your finger from Miss Manners' eye. Thank you. That is better.

The unpleasantness of being pointed at applies not only to strangers at a distance but also, you will be surprised to hear, to close-by acquaintances shouting "The error is yours!" However, you are correct that the error of pointing out errors to one's elders is worse. It is possible that just being adolescent is worse, even among those who keep their hands to themselves.

Q: I would like to have a wine-and-cheese party, but since I have never attended one, I'm unsure of the proper procedure. How many different wines and cheeses are served, and are they cut into cubes or slices? Also, I cannot justify buying 24 wine glasses for the occassion, so would the plastic champagne variety that can be purchased in a liquor store be acceptable?

A: Never attempt to slice wine, which is about as unacceptable as -- as forcing innocent people to drink from plastic glasses, particularly silly hollow-stemmed one that think they are hot stuff. At the simplest party (as opposed to the so-called wine tasting, which is usually a disaster), you need only serve one kind of each red wine, white wine, sharp cheese and mild cheese. You needn't cut the cheese if you provide boards and knives for such, and biscuits on which to dump the shreds. Cheap glasses are, in the long run, cheaper than plastic, the long run being your second wine-and cheese party.

Q: When I was a little girl, my great-grandmother gave us her hope chest and now that I am 34 and all my relatives have given up hope, I am actually getting married. My great-grandmother is long since dead, and even my mother said she never thought she'd live to see the day.

But anyway, my mother once promised to fill the chest with linens when I became engaged. I plan to hold her to this, although she claims that the decision, by me and the man I have been living with for 6 1/2 years, that we might as well get married, is not her idea of a proper engagement. While we fight over that, would you mind settling the next issue, which is bound to be: What does a proper linen trousseau consist of?

A: Do you mean that you are going to send Miss Manners out of the room to count the sheets and towels while such an interesting fight as you are having now is taking place? Oh, all right. She's going, she's going.

The linen trosseau is sub-divided into Bed, Bath, Kitchen and Table, of which Table (surprise!) is the most interesting.

Table linens

Is is well known tht no bride can enter matrimony with her head held unless she has a damask tablecloth and 12 dinner napkins, each 24 inches square, to match. It is well known that the bride never uses these items until her silver wedding anniversary, and that someone then promptly justifies her caution by spilling red wine all over them. Nevertheless, the cloth should be monogrammed diagonally high on one corner, and each of the napkins on the art that will show when the sides are rolled under and it is centered on the service plate.

A linen luncheon set, consisting of a tablecloth and smaller napkins (about 15 inces square) is also needed for those elegant luncheons that every bride rushes home from work on weekdsays to give seven of her closest friends. Linen or cotton table mats and napkins may be used for breakfast. An endless supply of teeny-weeny hor d'oeuvres napkins is necessary, as guests always put them in their pockets.

What about the wipe-off mats, brightly colored cloths and napkins that don't show stains, imaginatively used designer sheets for the table and bridge-size cloths that the bride will actually use? She buys them herself; those are not part of the trosseau.

Bed lined

Six sheets for every bed and three pillow case for every head (meaning six for a double bed) are the minimum and naturally they should be monogrammed. sHem-stitching, which rips off like perforated toliet paper, is nice, too. Miss Manners only allows white sheets, and prefers that the monograms be in white, as well.

Naturally, such a bed needs a silk or muslin blanket cover, and a bedspread.

Miss Manners likes covers to be monogrammed, but never bedspreads. Don't ask her why.

Again, all that permanent press, jungle patterened, mix-and-match junk you use for sleeping in, and the fitted, quilted things you use to avoid making the bed, are not properly part of the trousseau.

Bath linens

The most important items here are the linen face towles and linen hand towels, none of which are ever used, even by the guests. You are also allowed terrycloth bath towels and wash clothes, which are used, although what a respectable person does with the small terry cloth towels always sold to match, Miss Manners cannot imagine. Monogramming terrycloth strikes her as silly, unless you are a hotel with untrustworthy guests.

Kitchen linen

Lien towels are keeded to keep up the pretense that the bride will never put her fina china and crystal into the dishwasher. They have no other use. Rough towels and potholders are quite useful, however, which is why they do not belong in a proper trousseau.