AS A motivating force for unassailably correct behavior, jealousy, Miss Manners has noticed, is not a conspicuous success.

Why is that? Miss Manners should think that people who believe themselves to be on the losing side of romance would endeavor to make their behavior more attractive, not less, to their errant loved ones. And yet the usual procedure is for the person who suspects a waning of interest to adopt a mode of action so outrageous as to supply ground for dismissal on that basis alone.

Miss Manners has always believed jealousy to be a waste of time. She has never to known anyone to be the better off for having it. But if you must go in for it, she begs you to observe a few rules of decency.

It is important to identify correctly the object of your ill will. Too many people make the mistake of directing this to the person who got the promotion, rather than the employer who failed to give it out properly, or on the romantic replacement, rather than on the person who did the displacing. It is, in Miss Manners opinion, pathetic to see to women, for example, engage in a vituperative rivalry while the object of their dispute sits luxuriously on the sidelines, perhaps even urging each of them on in the fight. lDisgraceful, indeed.

The correcte attitude of one lady to another in such a situation is calm, polite and somewhat distantly cheerful. And since Miss Manners was talking about motivations for politeness, she will add that such behavior is very worrisome to anyone with rivalrous intentions. Why is she so unruffled -- is she really anxious to dump him on me?

As for the behavior toward the cause of the trouble, that, too, must be within the bounds of propriety. Faithlessness in one person does not absolve another from ordinary rules of good conduct. Lawlessness, usually in the form of some sort of spying, is not allowable. Miss Manners would even go so far as to say that evidence obtained by such means as opening another person's mail, reading diaries, going through pockets, or making disguised-voice telephone calls is not admissible when arguing the original crime. It can only lead to a mistrial in the matter of infidelity, with a new issue, that of unethical snooping, the subject next taken up.

Then there are the modes of behavior which are not exactly unethical, but not exactly attractive, either. This includes all material for 10-page letters and midnight telephone calls. Ladies and gentlemen do not threaten each other, and they do not attempt to force themselves on each other when they do not seem to be welcome. If this is true in social intercourse, it is doubly true in . . . in romance.

Miss Manners wishes that she could guarantee that the patient observance of excellent manners under trying circumstances would re-inspire errant lovers to know what treasures they are losing. She cannot.

But she does promise that no one was ever inspired to fall back in love because of a campaign of unrelenting persistence, or because of a threat of suicide, murder or financial ruin. MISS MANNERS RESPONDS

Q. Can you help us resolve a lively debate about the proper use of the waste bowl in a coffee service? At a recent elegant dinner party, one guest was certain that it should be used to hold hot water that has been used to "preheat" the cups. Another was equally certain that the dregs of one cup of coffee are poured into it before the cup is refilled. Our hotess was very uncertain, and admitted that she does not use hers for fear of doing so improperly. This seemed to us like the waste of a good bowl.

A. Quick! Stop! Please! Oh, good heavens, why didn't you call for help earlier? You are using a tea set to serve coffee.

Actually, Miss Manners can think of no good reason why you shouldn't. She just doesn't want to spoil that lovely party by siding with one friend against another. Surely, if you are all equally wrong, no one can feel hurt.

It also explains why there is a waste bowl, or as it is sometimes so elegantly called, a slops bowl. This is for the dregs of tea. A coffee set consists of three pieces: a coffee pot, a sugar bowl and a cream jug; a tea set has five pieces: a teakettle, for boiling water; a teapot for the tea, a cream pitcher, a sugar bowl, and the waste bowl. (Miss Manners is not counting trays, tongs, caddies, strainers and such, any more than she is counting the teaspoons, until after the guests leave.) If you can subtract, you can figure out how your hotess can have a perfect coffee set, free.

Q. I react to questions about my daughter-in-law and son from people who ask, "Well, any babies?" or "Are you going to be a grandmother?" etc., by glaring at them and saying, "I don't ask them such questions." Certainly it is not my business, nor anyone else's but even so perhaps I have blown this up more than is necessary. Is there a polite response?

A. One can hardly exaggerate the rudeness of inquiring into the contents of someone else's womb. Sooner or later, these people will get a burst of tears for an answer, from some couple unable to conceive a child. Miss Manners considers your answer, or a cool "I have no idea" civil enough, under the circumstances.

Q. Please explain the fingerbowl. I have not used any, but I am considering it, because I often serve messy foods, and it sounds like a sensible, practical idea.

A. Actually, it is not. Correctly used, the fingerbowl is a charming touch of no practical use whatsoever. When service is of a degree of formality to require fingerbowls, the food is never messy enough to require them. If you want to clean off your guests before dessert at an informal meal, offer them warm, damp, small terrycloth towels served with tongs from a wooden tray.

But Miss Manners must not get unpleasantly practical herself for forget that what you asked her to do was to explain the fingerbowl. Very well.

It is a small, individual bowl, usually glass but sometimes silver, with a glass lining, half-filled with water in which small flower petals are floating. gNo lemons, please.

It arrives on the dessert plate. For formal dinners, dessert service paradoxically consists of a lot of different things all stacked up together, just the way you told the children not to clear the table.

On the plate from which dessert is to be eaten are a crocheted doily, the fingerbowl, and, on each side, the dessert fork and spoon. The guest is then expected to set the table properly, placing the fingerbowl and doily to the left, and the fork and spoon on either side of the remaining plate, before taking dessert. What the guest does not do is use the fingerbowl as a sink. At the most, one can dab one fingertip in it, but many people consider even that vulgar. Fingerbowls are not for people who cannot tolerate anachronisms.