SOMETHING strange happens to children when they turn 13 years of age, but Miss Manners is not sure she would call it adulthood. Nevertheless, the special celebration of the 13th birthday seems as right to her as having New Year's in the crisp, begin-again air of autumn as the Jewish calendar does, instead of when the roads are already icy and dangerous. j

The Bar Mitzvah, for Jewish boys, and the less traditional (but only fair) Bat Mitvah, for girls, carries religious responsibility for the person who is coming of age. But no child should be considered to be legitimately approaching adulthood who has not also mastered some social responsibility. Celebrating a Bar or Bat Mitvah, whether by receiving the congratulations of the congregation in the synagogue or by being the guest of honor at a hotel dinner-dance for 400, is an excellent test of these skills.

No 13-year-old should be permitted to begin whining, "But I'm not a child anymore -- you always treat me like a baby," let alone to call itself by the dignified title of adult, without having mastered the ability to:

Accept the idea that no occasion, least of all a social event, is so important as to justify subordinating claims to the pleasure of one person. Life may often be a compromise, but parties always are, and learning this early will spare the child enormous, emotional grief on wedding days, inaugurations, retirement parties and whatever other milestones are stepped upon.

Realize that there is a relationship between the financial resources of the family and the amount of money it can spend. It is difficult to understand that money spent on non-pleasurable items for a child, such as shoes and tuition, have a connection with the amount of money available to spend on things the child actually wants, such as live bands and ski trips.

Analyze one's family and friends dispassionately in the interests of forming a proper guest list. For example, not being able to stand a certain relative counts for nothing -- the only thing that counts is how closely the person is related. There can be a cutoff on the family part of the guest list, but it is made on the basis of how much blood there is in common, not how many interests. While it is true that friends tend to be people one likes, there are often more important considerations, such as how close one's parents are to their parents, or whether invitations were forthcoming to their parties.

Accept a compliment, no matter how silly. The answer to "What does it feel like to be a (heh, heh) man, sonny?" is a smile.

Stand in a receiving line looking pleased to see everyone, no matter how detestable. Related to this is the discipline to circulate, in both talking and dancing, without distinguishing between the people one likes and the people one was forced to invite.

Perform introductions, fully and correctly. No person who cannot introduce to his grandmother the chief troublemaker of the eighth grade, getting the proper sequence and the correct name of each, and entirely concealing terror of what one might carelessly say to the other, can be considered an adult.

Behave as if age were not the single most distinguishing factor among human beings, and act as if it were perfectly natural to have a room full of people of different generations who are not even all related to one another.

Write prompt thank-you letters, each with an opening other than, "Thank you for the -- "

Miss Manners wishes you to note that this is a minimum list. If, on top of these skills, you can pile some grace and sense, she will promise to consider you as a full-fledged human being. MISS MANNERS REPONDS

Q. Will you please advise me how to address invitations to a couple who are separated, when you wish to invite both, each with a friend or escort? They are living at different addresses.

A. It should be an exciting party. Write to each separately, at each separate address, and state your invitations and the fact that they include the opportunity for each to bring a guest. It is, of course, common courtesy to inform these people that they will be confronted with -- and exposing their accompanying guests to -- their estranged spouse, but Miss Manners understands that doing so may ruin the fun you have planned for the evening.

Q. Please settle a small dispute between friends. She says there is no polite way to eat pomegranates in public, and therefore they should not be served.

I say that providing they have been completely peeled and the seeds separated, one can eat them, singly or in groups, and discard the pits, via a spoon, onto one's plate. Please don't answer that a squeezer would solve the problem by allowing you to have pomegranate juice.

A. Why not? Why should you have all the fun? If you are getting pomegranates, it seems to Miss Manners that you are having about as much fun as a human being can stand. The pomegranate is nature's little tease, inviting you to guess which parts of it are edible and which are not. Some people throw out the seeds and are sorry afterwards, and some eat the pulp and are sorry about that. The key still here is knowing how to admit defeat gracefully, which is to deposit mistakes neatly in the spoon and then on the plate, as you describe. If you can do that without making a face, Miss Manners will permit you to eat pomegranates, singly or in groups.

Q. I am applying to several schools, and they all ask some version of my life story, to be told in my own words, telling them about my interests and about why I am applying to their particular school. The truth is that my chief interest and my reason for applying is the same: I would like to get away from home. My parents and I don't get along, and now they are having a trial separation and I don't want to live through it with either one of them. I don't know that this is anybody's business, but I want to get accepted by at least one of these schools, and don't know what to put down. Do they expect you to be perfectly frank with them?

A. Of course not. They are looking for people who are smart. Your interests are one academic subject, one sport (preferably a team sport played at the school) and one cultural activity (preferably with no drug associations). Your reason for choosing each school is that you heard its fine reputation in each of these fields.