ALL THE dear little gentlemen who are now asking Miss Manners for the rules of etiquette for dating claim to have possessed this knowledge once, but to have forgotten it. Miss Manners doubts that.

If a gentleman was once taught proper dating behavior, there is no reason that a few decades of marriage and an unpleasantly contested divorce should have knocked it out of his head.

Here, then, are the basics of dating manners for teen-aged gentlemen. The ones who happen to be over 40 may substitute the word children for parents when studying how to treat the young lady's family.

There are three possible parts to a date, of which at least two must be offered: entertainment, food and affection. It is customary to begin a series of dates with a great deal of entertainment, a moderate amount of food and the merest suggestion of affection. As the amount of affection increases, the entertainment can be reduced proportionately. When the affection is the entertainment, we no longer call it dating. Under no circumstances can the food be omitted.

A well-planned first date, for example, might consist of theater, a concert or the movies, followed by a light snack, after which the dating couple lock eyes significantly and then part. In the middle stage, the entertainment may be encompassed into the food part, as in an evening spent at a restaurant or picnicking, and the expression of affection increases. In the last stages of dating, food comes last, but is needed in greater quantities.

But let us return to the earlier stages of dating, when practitioners of the custom display the most uncertainty. It is at this point when conventional patterns should be strictly followed as a safeguard against the premature expression of frank emotion.

To begin with, a specific invitation can, at worst, inspire a specific refusal, while a general invitation could bring on a general refusal. The reply to "Would you like to go to the circus with me a week from Thursday?" may be negative, but it is bound to be more bearable than a negative reply to "Would you like to go out some time?"

Upon acceptance, the lady is told the details of the evening. She needs to know the hours she will be missing from home, enough information about where she will be to satisfy the other occupants of that home and what the appropriate dress will be.

Gentlemen still pick ladies up in these early stages, and they still make pointless conversation with the other inhabitants of the house. The purpose of this is to reassure the lady's parents (children, roommates) and to give them some basis for understanding her evaluation of the date afterwards. That is why the conversation must be pointless. Pointed conversation, about politics or automobiles, for example, does not reassure them and will be used against the suitor later. If he feels at ease at this time, he is doing something wrong.

The hours of the date are respected at this stage. The gentleman picks the lady up when he said he would, and he brings her home when he said he would. He only enters the house afterwards on enthusiastic urging, he takes care not to disturb the other inmates, and he departs before it has occurred to the lady that it would be advisable.

The younger gentlemen no doubt are wondering now why all this politeness and gradualness is necessary, and why they can't just frankly get on with it. Miss Manners would be greatly obliged therefore, if the elder gentlemen would explain to them the principle of the prolongation of pleasure.

MISS MANNERS RESPONDS

Q: We are a pair of barflies who have been frequenting the same bar now for quite some time and have been repeatedly faced with a perplexing question. The owner, with whom we have become socially acquainted, periodically serves as our bartender. Our question to you, Miss Manners, is, does one, in such a situation, properly leave a gratutity?

A: So many difficult tipping rules are involved in this one situation that Miss Manners can understand your feeling tipsy. The first is that you tip the bartender. The second is that a friend acting in his professional capacity is compensated to the same degree as a stranger performing that service. The third is that the owner of an establishment is not tipped. Your friend will perhaps not thank Miss Manners for tipping you off to this.

Q: My daughter is being married in a fairly small, informal church wedding. We need to keep expenses as low as possible, but want the affair to be in good taste. Could you please answer the following questions:

If the bride wears a long gown but no veil, is it proper for the groom and the other men to wear business suits? Is it necessary for the bride to wear gloves; if so, should they be elbow length? Is it up to the bride's mother to determine what she and the groom's mother will wear (short or long dresses)?

A: It always amazes Miss Manners that people believe that spending money is in good taste. On the contrary, such terms as simplicity and understatement are code words for upper-class budgeting. What you should have for an informal wedding is dark suits for the men, short dresses for the mothers and no gloves for the bride, certainly not elbow length. If you will add this up, you will find that Miss Manners has saved you several hundred dollars worth of bad taste.

Q: I have recently been informed by a friend that, after a long hiatus, she has decided to re-enter psychotherapy. I was unsure of the proper response, and of how much to pry into the reasons behind this decision. As a number of friends and acquaintances enter and withdraw from psychotherapy periodically, this problem comes up fairly often. What guidance can you offer on the proper salutation in these circumstances?

A: The proper salutation to a friend is always "Hello; how are you?" but Miss Manners advises you to say it with as conventional a delivery as possible. The slightest trace of compassion in your voice may put you in danger of receiving a truthful answer.

Miss Manners does not say this to make your friend feel that you are cold, unconcerned and rejecting, thus giving her something new to talk about in her sessions. She is saying it out of respect for psychotherapy's use of the medical model.

People who are under professional treatment of whatever kind do not generally benefit from paramedical assistance on the part of their friends. The temptation to extract your friend's symptoms and then explain to her what is really wrong with her and what she should do about it should be resisted.

If you wish to hear about the problems of your friend's life, in your capacity of friend, that is another matter. Friends do not pry, and they offer comfort, not analyses, of complaints. It is to be hoped that your friend also understands that discussing one's operation in detail is a notorious abuse of friendship.

Q: No doubt you are familiar with those lists provided in most infant magazines, which describe in great detail the proper layette for baby. Well, baby is now 17, and has been admitted to one of those frightfully old and well-known schools in the Northeast. Yes, Harvard to be exact! Pardon me a moment while I attempt to bring my astonishment (and pride) under control.

Perhaps you might provide us with a layette list, telling us what is really in, behind those ivy-covered walls. How many tiny undershirts will he need? What about Levi's? And his Louisiana State Bird shirt, the one with the huge mosquito on front? A tuxedo? Sheets? Towels?

Friends have suggested that he make the necessary purchases when he arrives up North, but this child has great taste (if you know what I mean). Bankrupt City is not what we have in mind. Therefore I would appreciate having your list while there is still time to do some shopping here.

We are trusting in you, Miss Manners, to tell us the entire terrible truth. But please keep in mind that the child's father is a civil servant and his mother will be going back to work as a high school teacher to help meet the extra demands on an already shaky budget.

A: If you will cast your mind back some 17 years, you will recall that Baby's layette, cunning as it seemed when you assembled it, was of amazingly short-term use. Those wee sweet undershirts were too hot for him in the summer, unnecessary under soft warm clothes in winter, not dressy enough for visitors and too much trouble for the at-home look. He never even got a chance to wet or spit up on them all before he had outgrown them.

The same general principle applies to college wardrobes.