THE IMPULSE of expansive hospitality is such a charming one that Miss Manners would like to encourage it by showing how one can make hospitality somewhat less expensive. Ah, er, cheaper.

For while it is true that no form of social entertainment is quite so enjoyable as the "little" dinner party of 10 people, five courses and three wines (unless it is the private Aegean cruise, which is also a pleasant way to see one's friends), this kind of thing now runs into a considerable amount of grocery money. Nor does Miss Manners exactly believe all those articles about clever, thrifty cooks who make perfect souffles Grand Marnier out of discarded orange crates.

A simplier solution, it seems to her, is to invite people to visit you when they're not hungry. One cannot say, "Do come by some time when you're stuffed"; but one can learn to socialize at times other than the dinner hour.

Six to 8 o'clock at night is exactly when most people are getting ravenous, which is why the cocktail party has had to turn into a buffet dinner, and why you will find, after a "wine and cheese party" that all the paper doilies under the cheese have been eaten.

Four o'clock is much better. Bread-and-butter, cucumber sandwiches, cookies and tea will satisfy most people at that hour, and if they are also given an iced cake, one-inch square, and a thimbleful of sherry, they will consider themselves to have been treated lavishly.

(Just do not make the common mistake of calling this "high tea." High tea" is acutally a substitute for supper when the main meal is taken at noon, and anybody who knows the correct terminology will feel gyped if there is no meat, soft-boiled eggs or whiskey.)

There are other times, morning, noon and night to be exact, when most people actually prefer eggs, breads and salads to higher-priced staples.

There ought to be more weekend breakfasts and luncheons given anyway. Dinners represent a greater effort on the part of the guest, as well as on that of the host. One feeds the children first, dresses up, turns the children over to another keeper and goes out, committed for three hours or more. But a breakfast or luncheon invitation can be a welcome short break in an otherwise busy day, and children should be encouraged to come along (and then encouraged to "go out and play").

Light food also looks luxurious late at night, because even the greediest people know they are not really entitled to a midnight supper.

The way to get people to your house for a midnight supper is to invite them to something beginning at 9:30 or 10 -- dancing, for example, or an amateur concert given by friends who are good enough to be bearable but not so good as to become unbearable. Or can invite them to supper after a movie or play which they and you are attending.

For a really chic and cheap party, suppose you find out which of your friends have opera tickets and invite them to come home with you afterwards, adding: "We'll dress," which means that you are dictating the importance of an event for which they have paid. You then allow them to kick off their evening shoes and feast on scrambled eggs and cold wine. The least they can do in return is to invite you to vacation with them in the Aegean. MISS MANNERS RESPONDS

Q. I am an 80-year-old widow whose husband died last April, and I should like to know what is correct regarding my sending out Christmas cards this year. Usually, I send out about 40 cards to close relatives and friends, and in about three-quarters of them, I enclose letters and notes. Would it be correct to follow my usual custom this year, even though Christmas will be rather sad for me, or should I just send the letters and notes without the gay cards that I usually send?

A: You would never know it from all the complicated rituals of partying and present-giving associated with this time of year, but Christmas is actually a religious holiday. Therefore the notion that only merrymakers may participate is rather ridiculous, although many people seem to hold it.

Of course, you should write to your friends -- surely now, more than ever, it should be a comfort to be in touch with those you care about. And Miss Manners, feels sure that those who suppose it "tasteful" not to send cards to you this year because you are presumably not in a festive mood, are not going to impress you with their sensitivity.

The only difference is that one does not expect a bereaved person to overflow with merriment. A sense of gaity you do not feel would be inappropriate on your cards, and those sent to people in mourning should not display this either. But it seems to Miss Manners that it is possible to discover a spirit of Christmas besides that symbolized by little hiccuping Santa Clauses brandishing cocktail glasses.

Q: Your advice to the hostess whose friend falls asleep after dinner -- that she should quietly nudge or whisper him awake -- may be correct as far as manner are concerned, but you didn't really deal with the cause of the problem, which is probably medical. There could be many causes of uncontrollable sleepiness after eating -- the sugar in the dessert, for instance, or breathing difficulties, and it is extremely important that the person find out why he has this problem and do something to control it. A truly good friend would not only minimize the embarrassment when this happens, but afterwards urge the person to get to a doctor.