ENDING THE summer is easy. You will please put away your white shoes on Labor Day, and not get them out until next Memorial Day. Miss Manners does not want to hear any whining about hot weather, or pleading about clothing you still need to wear that requires white shoes. You have a few more days, and then that's it for the year.

Other endings do not seem to be quite so simple. Many people are unable to end anything, from a summer romance to a postal card, and Miss Manners has seen unfortunate examples of both dribbling pointlessly on because no one knew how to stop.

The best way to end a holiday romance is to get off a ship without having fulfilled the promise to write down one's address. This is difficult to do nowadays, because few people get on ships. The speeded-up version of the shipboard romance, the airplane acquaintance, hardly seems worthy of a bittersweet good-bye when a quick wave will do.

In any case, Miss Manners does not believe in ending a summer fling by explaining that it was a summer fling, when the other person might have considered it significant. Neither does one document the decline of one's interest; it is not nearly so charming a story as the build-up of feeling was, at the beginning of the summer.

There is no way to be kind in such an assignment, but you can at least be vague. You never know when you might want to get back to this some day, there being so much turnover in the modern romantic whirl as to keep Miss Manners' head spinning.

What needs to be made clear is that the romance is no longer the first priority. As any romance worthy of the name takes priority over everything else in life, including eating, sleeping and working, this should do it. The standard version is something like, "Well, let's give ourselves some time to get back into our regular routines, and then we really must get together. As soon as I'm organized for fall, I'll get in touch with you." A more drastic version of this might be, for example, "Let's see how it goes--things are bound to be a little different in the city, you know. I don't know if I mentioned that my family is there."

Ending a postal card is done even more abruptly. No sign-off statement, such as "See ya," is appropriate. Postal card messages are, in themselves, entirely composed of conventional statements, if not frankly inane ones, and to compound them with a expression of regret at the conclusion is superfluous.

Letters hardly need more. "Well, I guess I've got to go now," followed by a list of irrefutable reasons, does not enhance a letter, especially as the alert reader, having spotted the signature, is already aware that the letter is coming to an end.

"I hope you are well," "Give my regards to your brother," and "We all hope to see you soon" are, however, useful ways of toning down a presumably more exciting letter and preparing the reader for its conclusion. "Please write soon" is not so good. We do not nag our correspondents to reply to our own missives; they will, or will not, in due time, but the request is neither effective nor endearing.

On the telephone, a sign-off is often needed, as there are people who never will sign off otherwise. The placer of the call is supposed to end it, but if he fails to do so, it is permissible for the receiver of the call to remark pointedly, "It was good to talk to you." You will remember that Miss Manners always advises against explicit excuses, such as "I think I hear dinner boiling over," because some people will call back to inquire politely whether it did.

The general principle, you will notice, is that the less said, the better. When you have mastered all these techniques, Miss Manners will agree to tackle the compound question of how you end a telephone conversation from someone complaining that you didn't answer letters, which you omitted to do because you have tried to establish that the romance was over. MISS MANNERS RESPONDS

Q: Please help. As a bachelor, I attend a goodly number of socials, parties and dances. It is by no means infrequent at these gatherings to run into women I dated briefly before, but then either saw no point in calling again, or I did call but was refused. Now we're both back. What's the proper thing? Say nothing at all? Avoid their eyes?

Would your answer apply to the indiscretions where two people run into each other after a phone number has been given (or asked) for the purpose of getting together, but one of the parties changed his or her mind about getting together in the interim?

A: Miss Manners, who is occasionally given to woolgathering, has been set off by your question into imagining what you might say to these ladies as an alternative to "nothing at all" (which she interprets to mean having ordinary conversation without reference to previous relationships or the lack of them).

"The reason I didn't call you was that I fell in love with my landlady and I got too busy," or "Well, here we are again," or "Remember the time you threw my cat at me?" or "Why were you avoiding me?"

No. Old acquaintances are invariably greeted with innocuous remarks such as "Why, how nice to see you," and "You look wonderful." They don't mean anything and are, Miss Manners assures you, a lot safer than raking up unsatisfactory memories.

Q: My courtesy call on my 38-year-old son's fiance'e's family has been made. I liked them.

I became a widow last year. My husband had met this 31-year-old woman before he passed away. He knew Tom was planning to marry Mary and was very pleased about it.

You see, our son became a widower 1 1/2 half years ago -- his wife and the mother of his three teen-agers was a cancer victim.

My question is, should I send wedding invitations or just announcements? So many of my friends gave gifts to Tom at the time of his first marriage. These two have two households between them, so gifts seem almost superfluous. Still, I don't want to rob Mary of anything. Her happiness means everything to me. You see, I love and admire her so much. Could you please answer a confused mother who hopes and want to be a good mother-in-law?

A: Your letter is so full of kindness that Miss Manners will put very gently her usual tirade about the rudeness of being preoccupied with presents -- either because one anticipates them or because one wants to head them off -- on ceremonial occasions.

Which is more important to you--that Mary enjoy the full attention of a happy bride, surrounded by the family and friends of her bridegroom as well as by her own, or that some people may react to this joyous occasion by grumbling that they gave Tom a silver teaspoon 15 years ago (because he has teen-age children, his first wedding cannot have been yesterday) and grudge doing so again?

A bridal couple and their families should think of wedding invitations only as an opportunity to share the event with people they care about. Let the guests worry about the presents.

Q: Regardless of our role as host or guest, my otherwise charming and eloquent husband drops out of the dinner conversation as soon as his meal is placed before him. I know for a fact that he is neither starving nor a simple glutton; nevertheless, he proceeds steadily through each course, mute, leaving me to represent both of us in conversation. I am not a perennial chatterbox, so after everyone else has contributed their respective anecdotes, witticisms and commentaries, his silence becomes noticeably awkward. Friends have asked me later if something was wrong.

I have brought this habit to his attention, but he claims to be unaware that he is doing it, or that he has nothing to say, or that it should be of no concern to anyone else at the table. Needless to say, he is usually the first to finish eating, and I the last.

Please, Miss Manners, is conversation during a meal with relatives, friends or business associates strictly a matter of personal choice, or should it be expected that all parties participate in at least a minor way?

A: What you have there is either a man who has never learned to alternate chewing and conversing and is therefore afraid of talking with his mouth full or a good listener. It seems to Miss Manners that it would be more helpful to define him as the latter and teach him one simple trick.

Before getting down to the business of eating, he need only turn to the lady next to him and say, "What is going to happen, with the economy the way it is?" or "Here I've known you all these years and I realize that I know very little about you."

Then, if he will only look up with an interested expression now and then, he may enjoy his dinner in peace.