If you do not already have a strict family policy about whose business is whose when it comes to asking personal questions and giving advice, now would be a good time to formulate one.

Otherwise, Miss Manners will end up being too exhausted from picking up the pieces after your Thanksgiving squabbles to enjoy standing under the mistletoe at Christmas time.As everyone knows, the etiquette rules for relatives in such matters are different from the rules for people to whom one is less permanently and closely connected. Or perhaps everyone doesn't know that. An awful lot of families seem to run into trouble by assuming that there are no rules at all among intimates.

Isn't that what intimacy is? Not having to worry about making a difference between what crosses your mind and what comes out of your mouth?

Right. You are only too open to having your life probed and critiqued by your relatives. Then why do you dread gathering around the family table for another frank session?

Miss Manners' job, in regulating the querying and nagging permissible between one generation and another, has been made easier in the last few years by a phenomenon that has made life harder on everyone else. She apologizes for that.

The change is that it used to be only parents who fussed over children, probing to find out what their children who were too old to be supervised in person were doing, and advising them to stop. Or to start doing what they were neglecting.

Nowadays, it is only too likely that children are equally active in nagging and scolding their parents. The tone and fervor are the same; it is the choice of topics that is slightly different.

Miss Manners has noticed that the parents' usual agenda is sex and the children's is health. The fact that school systems have long used the latter as a euphemism for the former only adds to the confusion.

Favorite adult conversation openers at family gatherings include:

"When are you going to get married?"

"When are you going to get rid of that no-good so-and-so and find someone decent?"

"Don't you realize that you ought to be having children while you're still young?"

"Look at yourself - no wonder you haven't found anyone to settle down with."

Whereas the children would rather open with this sort of thing:

"How can you eat that stuff? Don't you know it's killing you?

"How can you eat that stuff? Don't you realize it's immoral?"

"When are you going to stop smoking? It's not only disgusting but it's endangering the rest of us."

"Look at yourself - no wonder you're out of breath all the time."

Ask people on each side about their own remarks, and you will be told that these are prompted by loving concern and care. Ask them about the other's remarks, and they will say that they are made out of spiteful nosiness.

Miss Manners is not going to step into the middle of that one. You should know better than she which areas drive your relatives crazy when probed, and what approaches are more or less successful with them. It would be sad if a stranger could tell you more about your own family's sensitivities than you have discovered by living with them.

So Miss Manners prefers merely to offer some guideline techniques for being on the giving end and for being on the receiving end of personal advice.

Unanswerable questions should be banned. "Why don't you get married?" and "Why are you eating that?" are not going to produce any illuminating answers.

People should be allowed to declare off-limit topics. "Look, I know I need to exercise, but I don't want to discuss it" or "I promise to let you know when we are going to have a baby, so there's no need to ask" are statements that should be honored.

Finally, Miss Manners suggests that everyone going to a family gathering keep repeating to himself or herself: "If they didn't love me, they wouldn't be interested. If they didn't love me, they wouldn't be interested. If they didn't love me. . . ."