GOSSIP IS now the national sport, having narrowly edged out the previous favorites, baseball and hanging around. But there does not seem to be any general agreement on the rules, let alone good sportsmanship.

This is a serious problem. We all know that gossip does not consist of excited whispers about how well someone is behaving. Therefore, we prefer to tell our own stories ourselves and let others furnish the subjects for gossip.

The astute will be able to figure outfrom this that gossiping is a dangerous sport. If the person it concerns is not going to like it, and if, by its very nature, it gets around and is likely to get back to that person -- well, the only wise course is not to do it at all. This is equally true of extra-marital sex, and the warning has about as much effect.

The question to ask oneself before indulging in gossip, then, is not so much, "Is it true?" or, "Is there any useful reason for repeating it?" (no, and no again) but, "Is this likely to come around again and hit me in the face?"

Yes, it is. But applying some discipline to the exercise will minimize the blow. of gossip, with the safeguards that should be used for each.

Gossip about oneself: This is a peculiar form of gossip, as the repeater does not call it that -- he calls it a "confidence" -- and does not understand that it becomes gossip the minute it has left his mouth. The only precaution one has against making one's confidences known is to keep them confidential. Promises extracted from the hearer mean nothing; if you haven't been able to resist telling, why should he? As dear Erasmus said in "De Civilitate," "It is safe to admit nothing that might embarrass one if repeated."

Gossip one has heard firsthand from and about someone one knows: This is the receiving end of the first category, and is considered quality gossip because it is presumed to come from an informed source.However, it is the worst gossip to repeat as the subject can also trace the gossip source. Repeating it and asking one's listener not to do the same is ridiculous. Skip this category and move on the next.

Gossip received secondhand about someone one knows: This is the best, as you can pass it on along with the name of your source, who will then be blamed for blabbing. Gossip this far removed from original research also makes better stories, as the facts are flimsy enough to be bent into whatever shape you need to make the story illustrate a larger truth about human nature. Just make sure you're not telling it to someone who is in a position to know the information better than you do.

In other words, find out first if your listener is the brother-in-law of the person you're gossiping about.

Gossip received secondhand about someone you don't know: This is celebrity gossip, and the best kind. It is highly unlikely to be true, as all celebrity gossip is made to fit a pattern of simple irony and assumes that people are always the opposite of what they seem. But it's a lot less likely than the other to get back to them and inspire them to get back to you. MISS MANNERS RESPONDS

Q. I hope you can settle an argument that has been going on for months. My boss says that when a man and a woman enter the room at the same time, or when passing on the street, the woman should say hello first. Also, if a woman is with an escort and passes another man, who should say hello first? The man or the woman? I say it is proper etiquette for the man to say hello to the woman first. We are waiting for your answer.

A. All right, but it's not going to end the argument. You are both right, or, looked at another way, both wrong.

The European custom is that men greet women first, the American custom is that women greet men first. As neither is much observed in either locality, you may choose the one you prefer.

Q. Every year on our wedding anniversary, my husband likes to wear some strange outfit to dinner to remind me that my "real husband is not so strange at all." One year he was Mickey Mouse; another year, he was Sinbad the Sailor. It's funny, sure, but I think it should be a time for romance and tenderness. It's especially embarassing when we celebrate with another couple. Is his "act" ill-mannered when we invite someone else over? How can I tell him without hurting his feelings? What should I do?

A. Miss Manners hesitates to suggest "doing" anything that would interfere with such an exciting marriage. If there were any husband a woman would have to decide to love uncritically or to leave immediately, it would be a husband who dresses up as Mickey Mouse. If you have any desire to celebrate one more anniversary with this man, Miss Manners recommends that you declare it a costume party and wear a polka-dot skirt, white gloves and black ears.

A. Acting very badly is not difficult, and many people to it professionally, although Miss Manners cannot tell you how or why they are paid to do so. What she can tell you is that true acting is a rigorous art for which one prepares oneself by observing human behavior in life, as well as in books and plays, and by acting on stage in as many roles as possible -- big, small, sympathetic unsympathetic, glamorous, character and so on. You begin in school plays or community theater, and continue in a college or graduate school that has a good drama department. You might also practice offstage. If you can act like a lady, for example, it will be considerable achievement.

Q. We understand your point about not putting "No gifts please" on our 50th wedding anniversary invitation. But if some of our guests do bring gifts, what is proper? Do we open them at once, later on in the evening before all the guests, or the next day in private? We don't want to embarass the guests who don't bring gifts.

A. This is precisely why bringing presents to parties, unless they are children's birthday parties or bridal or baby showers where opening them is part of the entertainment, is a terrible idea. Any other presents should be sent, so that a person who is trying to give a party or get married or whatever can have her hands free. If people bring things anyway, thank them and put the package aside while you are greeting other guests. If there is a moment in which you can open such a present inconspicuously, do so and thank the giver quietly. If not, open it after the party and write a note.