TO SAY THAT public parks are for everyone to enjoy would be, in Miss Manners' opinion, an excess of democracy. There are certain people whose hobbies ought to be enjoyed anywhere.

Muggers, for example, do not belong in public parks. If they must mug, perhaps they could agree to do it among their own friends of similar inclinations in the privacy of their homes, but Miss Manners doesn't want to know a thing about it.

She does feel that practitioners of wholesome, legal and mildly illicit pastimes could do better at sharing public park space if only they would learn a little self-restraint and tolerance.

It is rude for any one generation or group of hobbyists to monopolize the common greenery. Properly apportioned, even a small park should be able to accommodate abbreviated versions of the basic pleasures of different stages of humanity, and even a few of its more complicated satisfactions.

Perhaps there are items that Miss Manners has missed in her list of the great mild joys of life: Eating, reading, kissing, exercising and sitting around doing nothing. But these are ample to sustain a happy life, provided that one occasionally goes off and does something dramatic, such as winning a professional prize or having a baby -- and those things cannot or should not be done in the park.

Those who eat, exercise and kiss must contain their activities in such a way as not to offend one another or those who are sitting or reading. Eaters must not leave garbage or wrappers about. Exercisers must not send balls spinning into the laps of nonplayers. Lovers must keep their behavior such that a child who inquires, "Mother, what are those people doing?" can honestly be answered with, "They are kissing each other."

This is the park land equivalent of the greatest rule of etiquette: Don't scare the horses in the streets. Do not frighten the crickets in the grass.

This means no lewdness among those sunning themselves. In truth, Miss Manners has seen little lewdness among babies in their carriages and old people on benches, and not even much among the sun oil types lying in the grass. She just thought she'd mention it.

Noise obscenity is more of a problem. The natural noises of a park range from the sounds of children who wish to dramatize the damage done when a knee is scraped, to conversation, laughter and muttering. A little singing and a folksy musical instrument can usually be tolerated, but transistor radios, on the one end of the scale, and tuneless hummings, on the other, are too maddening for public consumption.

This brings us to the question of more energetic activities, such as begging, handing out political or religious leaflets, and that old park standby, shouting at no one in particular.

Miss Manners, straining herself to understand the meaning of that strange concept, the public, does not rule these out altogether. Presumably there are those among any park population who will welcome the opportunity to make contributions to charity, alter their religions or politics, or receive dire and urgent warnings.

She only asks that people present these opportunities in such a way as not to embarrass those who do not wish to take advantage of them. If you have urgent business to conduct in the park, it should be done discreetly and in such a manner as not to offend anyone. This is a rule that any self-respecting dog follows in the park, and Miss Manners expects no less of the public. MISS MANNERS RESPONDS

Q. We love to take elevator rides but the mean manager won't let us. It is the only building around with elevators. How can we take elevator rides? Thank you for answering our letter.

A. Thank you, sweet little children, for asking so nicely. Now stop tying up the elevator, will you?

Q. Concerning manners in the driver's seat, it seems that many people are unaware of what to do when someone confronts them with their high beams on at night. The common practice is to get even, which is stupid because most people simply forget and a gentle reminder -- flashing your high beams on and off quickly -- is usually enough.

Another case of extremely bad manners is those shopping carts strewn all over parking lots, especially the one I always see in the spot closest to the store on a rainy day. I've even seen carts roll onto a busy highway. It's simply a matter of habit and the exercise won't hurt, to put the thing back where it belongs.

A. Two excellent points, Miss Manners is always against the practice of getting even for rudeness received, but even her insurance company agrees that retaliation involving automobiles is not a clever idea.

Q. What do the respective parents of the prospective bride and groom do when the latter finally state that they are going to be married in August and they have been living together in Wyoming for a couple of years? We dare not question why they are waiting until August to tie the knot. Should we have a quiet dinner in a fine restaurant, just the four of us? I am sure you will be receiving more questions like this, since this is 1981, after all.

Should we call on one another? Should we have a tea? What? The couple are both fine, bright people. However, they do not carry on traditions which we did in 1955. Should we go to the wedding? Please help.

A. Miss Manners is not sure how much you carried on in 1955, but to her, marriage is still marriage, no matter what has been going on in Wyoming beforehand.

It is, therefore, still appropriate that you have a ceremonial family dinner with the young couple, that the parents of the prospective bridegroom call upon you, that you give an engagement tea, and perform whatever celebrations you would consider fitting upon the approaching union of fine, bright people. Of course you go to the wedding.