DILIGENTLY AS Miss Manners has been doing her research, she has been unable to discover any truly new inventions in the relations between the genders during the 20th century.

Sex seems to have been invented quite a few generations ago, contrary to the popular belief that it first occurred on the evening after one's own parents' wedding, but that its full potential was only realized when one came of age oneself. Apparently even primitive people long ago managed to catch on to the general idea and even the standard variations.

Therefore when Miss Manners is asked about the horrendous problems arising from Modern Sex, she has a difficult time concealing a weary little smile. The only modern development she has observed is the custom of self-gossip -- that is of making one's own activities so public as to force people who had been perfectly aware what was happening but essentially uninvolved, to take stances of approval or disapproval. In Miss Manners' opinion, this contribution has not made the world go around any faster.

Other so-called inventions turn out to be cases of historical ignorance. Take, for example, the "modern" matter of ladies asking gentlemen for dates. Have you ever heard of "I find I have an extra theater ticket for Thursday night?"

Yet one is continually hearing of ladies who are puzzled about how to take the initiative, and gentlemen who are bewildered about how to respond. Many ladies are unable to take no for an answer, and many gentlemen unable to give it.

The niceties of the pursuer and the pursued are well known in the society, and there is no excuse for those who have practiced one side to botch things and plead ignorance when playing the opposite part.

Miss Manners has no objection to a lady's initiating an engagement, provided she does so in the dignified, straightforward way that ladies have always appreciated in gentlemen. This means that one suggests a specific date and activity, and is gracious if it is declined. After three separate refusals, one stops asking.

Gentlemen should realize that it is perfectly proper to refuse such an invitation politely if one is not interested, and that elaborate excuses need not be given.

Why is it, then, that a lady who knows what it is to be pestered with unwanted attentions does not know how to shrug and accept fate when her advances do not meet with success? Continuing pursuit or turning bitter and rude is not gentlemanly, she should know.

And a gentleman who knows what a rebuff is will sometimes yield to the attentions of someone he doesn't really enjoy simply because he feels put on the spot at having been asked. He should know that it is a lady's prerogative to say no.

They should both know that sexual attentions should never be demanded or given out of the disgusting notion that they are a return to the person who pays the entertainment bills.

You see, Miss Manners has nothing at all against modern trival variations on behavior, provided the traditions are observed. MISS MANNERS RESPONDS

Q. Please help me to correct my fiancee and her mother on a point of etiquette. I have generously refrained from interfering with their preparations for our wedding thus far. Regarding invitations, however, I dared to speak my piece: Guests must be sent maps if they are to find the church. Aimless wandering about will not do.

My fiancee and future mother-in-law, however, insist that the insertion of maps ruptures the formality of the invitation, sending our wedding into the depths of boorishness. Should I return to passive acceptance of the rampages of two women gone mad?

A. It may reassure you to know that this particular form of madness -- the abandonment of all common sense in the desire to conform to a concept of rigid correctness in matters on which there is, in fact, nothing at all written in stone -- is nearly universal, but temporary. It is possible that if you lie low, you may find yourself ending up with a wife and mother-in-law as sane and reasonable as they were when you first suggested the relationship.

It is also impossible that you will find yourself being married in an empty church. Miss Manners sees nothing wrong with including maps, but if that drives them madder still, you might suggest a separate mailing of maps -- or just do one yourself.

Q. Today's society is certainly permissive, which enables me to bring a gay male date to family, social and business functions. However, there is always a question as to introduction and seating arrangements. My date is explained as a "friend," and we are seated as far away from each other as possible. It seems there is a limit to society's acceptance. My question is: What is the proper seating arrangement and introduction? And could you please give further etiquette rules governing the behavior of gay couples in the family, social and business functions, and also the behavior that should be extended by the host, hostess and other guests.

A. What is it that you want? To be introduced as lovers, with some explanation about your feelings for each other? To sit together and chat, if not hold hands, instead of socializing with other people?

The rule is that those who wish to be accepted in conventional society must accept the conventions of the society. This has nothing whatever to do with your private emotions, activities or living arrangements, but everything to do with society's failure to recognize non-legal relationships, homosexual or heterosexual. No other liaisons are part of conventional introductions, although you may confide what you wish to whomever you like.

As for not seating you together -- why, you are being treated exactly as a married couple. People who live together should be prepared to mix with others when they go out, and their pleas of being in love -- Miss Manners also hears such bragging from married people occasionally -- only make her wonder why, then, they don't refuse all invitations and stay home and enjoy themselves.