OF ALL the social rituals practiced in our civilization, the birthday party for young children is by far the most revolting. It must be endured, however, because it is a learning experience.

Miss Manners is, of course, referring to the lessons to be learned by parents who partake in such events. Children occasionally also learn something, such as how to control their rage and smile weakly after a parent has loudly and publicy inquired, "Did you say thank you?" but that skill is hardly worth the event. Certainly no child has learned from social exposure to produce an intelligent answer to the question, "What does it feel like to be 40?" Perhaps the fault is in the question.

It is the adults, the parents of the birthday child, who learn most from the experience, sometimes such handy information as the replacement value of their property. The smart ones also learn quickly to find sites for parties other than their homes. (The behavior of children at a birthday party is not necessarily a result of their being badly brought up. Group dynamics nullify the results of discipline, and six well-behaved 6-year-olds is the social equivalent of 600 angry Bolsheviks.)

Parents learn social planning through these parties, which requires both precision and flexibility in amounts never dreamed of by those who have mastered giving seated formal dinners for 18.

The minimum time for which one can decently invite guests is two hours. Children do not engage in the activity of "chatting," the standard fill-in between chewing periods in adult entertainment. for that matter, they cannot be depended upon to consume time, or sometimes even food, at chewing time. A party of children under 10 years of age will spend an average of 12 minutes at the luncheon table, including the time taken up by one child's explaining to the resident parent exactly how his allergies match the menu.

Parents also learn rehearsal techniques when they instruct their children on that great social skill, faking pleasure, as it is applied to duplicate presents and wallflower guests. The parent then enjoys the sensations of a theatrical director who stands at the back of auditorium on opening night, watching everything he has attempted to do go down the drain. A parent must also learn the restraint of a director, who usually controls himself from rushing costage to correct everyone.

But the most important lesson to be learned by the host parent is what it feels like to:

1. Look out the window with a child at the appointed time of arrival and not see anyone at all running up the steps with a package under the arm.

2. Look out the window at the appointed time of departure, your living room full of chaos behind you, and not see any other parents trudging up the steps.

If the parent learns to deliver and fetch his own children on time when they are attending another child's birthday party, it will have been a successful learning experience. Miss Manners Responds

Q: My girl friend and I are planning to do some travelling together, but we are arguing about how we should register at hotels. I don't see anything wrong with using both our names - we live together and are not ashamed of it at home. Also, even some married couples use separate names. But she says the hotel clerks would spot us and maybe not even rent us rooms unless we register as "Mr. and Mrs.," which I don't want to do because it's a lie.

A: Hotel clerks tend to be amazingly less fascinated with the marital complications of transients than the couples themselves imagine. You may sign your own name only, with the notation that the room is requested for two - if you don't think that would take all the fun out of it.

Q: People have been leaving obscene messages on my answering machine. I even recognize some of my friends' voices. In fact, hardly anyone has the decency to leave a regular message - just name, telephone number and what they want - which is what I bought the machine for. Instead, they make jokes or just hang up - or talk dirty. Don't they have any manners?"

A: You seem to be taking all this personally. These remarks are addressed to your machine, not to you. The standard of politeness one must extend to a machine is not at all the same as that expected toward a human being. Ask yourself whether your machine has any manners - issuing orders and beeping at people, as if it had been brought up in a barn.

Q: The people I was visiting last night asked me to put out my pipe during dinner. I wasn't blowing smoke in anybody's direction . They said it spoiled their food. I say it adds to my enjoyment of the food, which they ought to want me to have. Who is right?

A: Smoke is used to preserve food or to add flavor to it. If the food you were served required one of these functions, you were right. If it did not, the people who prepared it may rightly be offended at the suggestion that it did.

Q: Do you have to invite the same number of men as women, or does it matter if you have more of one sex than the other?

A: It depends on the sort of activity to which you are inviting them. If the activity is to be conversation, it doesn't matter.

Q: What do you do with tissues, after you have blown your nose in them, when you are out in public or at a friend's house?

A: For such occasions, you employ a cloth tissue, a clever little invention that is a square of cotton or linen that may be conveniently carried in the pocket and reused throughout the day. One should never begin the day without a fresh one of those concealed about one's person. Consider, for example, the difference this would make if you should have occasion to weep in front of others.Weeping into paper is disgusting: weeping into fine linen is romantic drama.

Q: Can I knit during social events? I like to keep busy when a few of us get together for coffee, but sometimes people think I'm not paying attention to what they are saying.

A: Miss Manners knitted all through classes at Wellesley, and at the end of four years ended up with both an education and a sweater that were service-able but somewhat smaller than she had imagined. Whether you can manage both is something only you know; Miss Manners only advises you not to explain to friends that you wish to do something useful while listening to them.

Q: I was staying with some friends for a week out in the country at a place they have, and a very close friend of mine called and asked if he could drop by because he had some business in the nearest little town. The people I was staying with had plenty of room, but acted funny when I asked if he could stay over. We were college roommates, and it seemed perfectly natural. Was I wrong even to ask?

A: Guests having guests is like pets having puppies - it is bound to be an unpleasant surprise to those who give them shelter and should be curtailed as much as possible.