IT IS either sex or kitchen machines. Miss Manners is not sure which is to blame, but something is killing off the Perfect Little Dinner Party.

The most recent incarnation of this exquisite ritual did not last more than a decade. As Miss Manners chronicles socialy history. Perfect Little Dinner Parties were actually being given all over America from the mid-1960s to the mid-1970s. They were preceded by a period of several years in which fashionable people claimed to be giving them, and followed by the current period, during which everyone claims he is about to give one again, just as soon as he can find the time.

In the first discussion period, in the early 1960s, the correct social statement was: "I hate cocktail parties -- charity balls are such a bore -- my idea of a wonderful evening is get together six, certainly not more than eight, close friends, so there can be real conversation." All the people who gave and attended cocktail parties and charity balls said this. Some of them gave dinner parties, too, but for fewer than 40 people.

Whether it was one of these people who got the idea of giving a Perfect Little Dinner Party from hearing himself talk is not clear. There were a nember of signficant socianthropological dinnovations at once, such as the long woolen skirt, the Lillet, and the printed bed sheet that could be used as a tablecloth. The result was that the PLDP was being given all over Amercia.

And a pleasant way to spend an evening, it was, too. It was discovered to be possible to socialize while sitting down, and some people even began to talk to those next to them once the possibility of their finding someone better was cut off during the dinner hour.

Now this custom is disappearing. (The exact dinner party figures will not be out until after the 1980 census is taken, but you may take Misxs Manners' word for it that the lovely one you gave just the other week is an exception.)

Miss Manners' suspicion about the kitchen machines is that they have created impossibly high expectations in the food department. The rise of the dinner party was naturally connected with the resurgence of interest in food (and the demise of that dreadful and ubiquitious objedt known as a "roast"), but once the number of blades a person owns exceeds the types of food he can think of that may be chopped, sliced pureed or beaten senseless, the challenge becomes too difficult.

As for the sexual element, that has become even more complicated than the kitchen equipment. The PLDP required assembling enough people to go around a small table, alternating genders. It meant that not only were guests required to come in mixed pairs, but that the pairs had to remain constant for two full weeks, that being the time form the invitation to the event.

Miss Manners is not saying that life is not more interesting now, with the variety, originality and independence that goes into making up social units of one or more. She is merely pointing out that symmetry ad predictability were essential qualities in PLDP guests.

Nor is Miss Manners requiring that you curb you little appetites and experiments in order to save a valuable social ritual, although it may come to that if we do not find a pleasant form to replace it.

At the moment, Miss Manners' proposal is Sunday teatime. This is an event to which people may be invited in numbers that do not exceed the number of chairs normally in one's drawing room. The best fare for it is simple to provide -- tea, sherry, cucumber sandwiches and cookies.

And one does not need a license, mechanical or marriage, to participate.

MISS MANNERS RESPONDS

Q: At a recent awards ceremony, just as the awardee was about to thank the awarder, a member of the audience took it upon himself to respond. What would Miss Manners consider an appropriate riposte to such boorish behavior?

A: The respondee should have been publicly thanked, immediately after saying, "I would like to add a few words." Miss Manners has always been mystified by what God had in mind when he implanted in mankind a love of making speeches without implanting any corresponding love of hearing speeches.

Q: Last night I ran into a classmate of mine whom I haven't seen in 10 years. I know hehs a writer now, but I didn't feel I could say anything about his new book because I haven't read it and he would be sure to find that out if I tried to talk about it. And yet I feel I should have said something, if only because he didn't mention what he was doing and seemed to be waiting for me to acknowledge that I knew, if you know what I mean. Waht is the right thing to say to an author when you can't honestly say "I loved your book?"

A: Few people, and no writers, have such high standards about compliments as to accept only those that will pass a rigorous test for veracity. Miss Manners' exprience is that an author will accept with joy any remark except "How many have you sold?" or "Did you know it's being remainedered now? " or "I'd love to read it -- please send me a copy."

Q: A friend called me at home (I did not call her) and proceeded to eat a raw carrot during the entire conversation. I tried to ignore the sound, but I found it extremely unpleasant to have to listen to a series of loud caracks and crunches while talking, ignoring the question of whether of not it's polite to eat while talking on the telephone (I assume it's not), would it have been polite for me to say, "Call me back when you're finished eating?" I don't like to hear dinner noises unless I am actually there to enjoy the food.

A: Miss Manners is in complete agreement with you except in the matter of taxing people directly with their social errors. She prefers an obluque line of accusation, such as, "Would you mind calling me back -- we have a bad connection. There seems to be a carrot on this line."

Q: I start work fairly late -- 9:30 in the morning -- and by the time I get on the bus, it looks like a trash basket. The early commuters all read the paper and then just leave them all over the place. I carry mine off the bus with me when I'm finished, and throw it away. There are public trash baskets near practically every bus stop. Why can't people use them?

A: Why can't people recycle their reading material? Miss Manners would like to see baskets placed at the doors of buses, in which riders may place their discarded magazineds or papers or morning mail, and other riders may find something to read. At the least, Miss Manners hopes that you discard your paper neatly at the top o the public trash container, so that anyone who happens to be browsing inside will find it in legible condition.

Q: Is it proper for one to eat while in the public right of way? Are fruits and vegetables fine, but not fried chicken? Of course I carry a napkin and do not litter with my leftovers, but what is really correct? Tomorrow's breakfast may depend on your response.

A: Dessert is the only course that may be properly eaten on the sidewalk, and only certain desserts, at that. Apples, bananas and pears are acceptable, peaches and grapefruit are not. Ice cream cones and chocolate bars are fine, but pineapple upsidedwon cake is out.

You will notice that dessert means that no meats or vegetables are permitted, nor are the usual breakfast foods, such as pancakes with maple syrup or eggs once onver lightly.

Q: A woman I met at a party asked me to guess her age. I thought she was about 40, even though she was wearing a satin disco dress and carrying a pocketabook shaped like a heart, and said so. Well it turns out she's 33 and is always being asked for proof that she's of legal drinking age, so I was supposed to guess that she was a teen-ager. I felt trapped by the whole thing. What should I have done?

A: You were trapped, so you might as well have gone along with the silly game. Why didn't you demand to see her teeth before answering?

Q: What the crime rate now, lots of people have those little peep holes in their front doors and refuse to open the door until they,ve had a look at you. I've even had to stand there while someone who has invited me to come just at that time fusses around behind the door, obviously there but not planning to open up until they've checked me out. I find all this disgusting. What can we do about it?

A: What do you find disgusting -- crime, peeping or standing outdoors? Miss Manners is happy to deplore any one of these things with you, provided you tell her which one. As for what to do about it, why you just step back far enough to present a head and shoulders view of yourserlf and smile in a dignified way.