Beware the Ides of March, all the signs cautioned Caesar. But Caesar, like the rest of us, marched straight past the warnings and into disaster.

It is not only Caesar who met his end on March 15. So did a 17th-century physician and cookbook writer named Sir Theodore Mayerne, who went under at age 82 following an evening in the company of convivial friends and unconvivial wine.

"Good wine is slow poison: I have drunk it all in my lifetime and it has not killed me yet; but bad wine is sudden death," said the good doctor, breathing his last.

Beware of bad wine and bad friends and a multitude of other things that can trip up a person on the way to a party. Who is coming for instance. Or who isn't. In Washington people rarely respond, no matter how firmly one underlines RSVP. And requesting "regrets only" makes it even less likely that guests will let you know. When people don't have to commit themselves, they don't.

One host who had sent out 150 invitations to a cocktail party had, by the day before, heard from only 15. He could not assume that the massive affair had been reduced to an intimate evening. Nor could he assume that all 150 would show up. Indeed, he could assume nothing and the only way he prevented a disaster was to pick up the phone and call each unresponding guest.

It was that or the possibility of having to freeze a year's supply of leftover shrimp puffs and Swedish meatballs.

But even the check-up phone call is no guarantee. In Washington, with politicians skidding off in all directions and aides and journalists following them, it is often impossible for people to tell if they'll be free until the last minute.

"I've never given a dinner party where I was really sure how many people were coming. The worst was when I didn't know whether it would be five or 15 until 7 o'clock on the night of the dinner," says a hostess who's learned to avert disaster by always inviting a nucleus of people who are sure to show up and then planning meals that can expand or contract on demand.

Pity the party giver. Not only is it necessary to figure out who's coming, but it's also the host's duty to tell guests what to wear. This is difficult for some Americans, who refuse to admit that they entertain formally. In their democratic souls, they are Jacksonians at home with the mob. If, in truth, they lean more toward candlelight and caviar, you'll never get them to admit it. When an unwary guest asks how to dress, the host invariably announces that the evening will be "casual."

Enter guests, he in corduroys and a sports jacket, she in slacks and a sweater, to find themselves surrounded by men in dark suits and women in satin and silk. The host may not mind a bit, but the guest does. One man caught in that trap reports that when he sat down to dinner, he tried to explain to his elegantly dressed dinner partner that he had been told to dress casually.

"Don't bother to explain," she said repressingly. "It's obvious that you're making a social statement."

Another man, put in a similar position, brooded for several days and finally sat down and wrote his hostess a furious letter, quite rightly blaming his embarrassment on her.

By telling a guest honestly what you expect other people will be wearing, you're offering them the choice of blending in or standing out: The choice should be theirs, not yours.

This, of course, does not count the instructions "informal" on official invitations. Most people who have been in Washington any time at all realize that this frees them from black-tie, but does not indicate cutoffs and T-shirts.