WHEN BRIDAL couples invite those who are dearest to them to share the public solemnization of their happiness, they may be sure that all their cherished friends and relatives are having the same thoughts:

Do we owe them a present? How much do you think we have to spend? Can't we get away with less? How much did they spend for us?

In a society that uses the terms "free gift" and "mandatory donation," it is not surprising that the exchange of presents is treated as an unpleasant commerical transaction, while impersonal fees are disguised as voluntarily given presents. Miss Manners once tried to step into the Metropolitan Museum of Art in New York after having discovered that there was no admission charge - only to be detained by an employe who admitted one could enter "free," but explained that that could only be done after one made a voluntary donation to the museum.

Miss Manners naturally inquired as to the meaning of such a voluntary donation.

"What do you want to give?" this person countered.

"A wing," replied Miss Manners, who was explaining that unfortunately she had not yet saved up the cash to carry out this wish, when she was interrupted with the information that intentions aside, she must give $2 on the spot or vacate the premises.

That is voluntary gift-giving in commercial life. In social life, however, there is no such thing as an obligatory present. You do not owe your friends $2 or anything else just because they are getting married.

Nevertheless, it is customary that when one values people enough to want to participate in occasions that are important to them, one is moved to express this emotion in some tangible form.

Get that? In other words, if you do not attend a wedding to which you have been invited, or attend only the ceremony and not the reception, you are not considered involved to the extent of, say, a silver bud vase. However, if you want to partake in the couple's bliss, and also their champagne, this restraint would be inappropriate.

The same principle may be applied to other occasions. You must care enough about people to want to gladden their hearts with a token of their esteem if you accept their overnight hospitality, celebrate their birthdays, graduations or Christmas with them, or expect a large inheritance from them.

Miss Manners Responds

Q: My husband and I sleep in a double bed at home, and would like to do so when we travel. We always seem to be put in room that either have two single beds, or two double beds. The single beds are too small, and I get embarrassed to have the maid see that we use only one of the double beds, so I've even taken to messing the other one up to make it look slept in, which my husband says is silly. How can I get the kind of accommodations we want?

A: By requesting them. If you find that this embarasses the room clerk, you might introduce him to the hotel maid you think is also capable of embarrassment, and suggest that they both take up another line of work.

Q: Is there any correct form associated with the chewing of bubble gum?

A: Yes. One must remove pink bits of burst bubble from one's nose quietly and quickly.

Q: What are the rules for how to administer recreational drugs at parties? Should the host and hostess provide the materials? Should they be passed about in the living room or should the guests retire to a small bedroom? Our 14-year-old daughter is a dealer. She says that her friends' parents are buying enough for the whole party.

A: Miss Manners is not amused.