Americans, always anxious to put their guests at ease, are doing something terribly rude. They are putting Their Royal Highnesses Charles and Diana on a nonstop diet of Brussels sprouts.

That takes some explaining, and here it is.

My wife and I were traveling in West Africa a few years ago when we bumped into an old friend, a former ambassador to Washington, who instantly invited us to join him for dinner at his sister's.

He satisfied us that our unannounced arrival would cause no problem whatever, and so we went. The sister was distraught. All she had (albeit in copious quantities) was palava sauce, stewed fish and an assortment of the other West African delicacies my wife and I had learned to love. Why, she demanded, hadn't our friend called to let her know he'd be bringing American guests for dinner?

"Because," he said, "you'd have run off to the market to buy Brussels sprouts."

Since then, Brussels sprouts have been for us the symbol of too much making one's guests at home. Americans have been buying up tea and biscuits, Pimm's Cup and, for all I know, stove-top Yorkshire pudding in the hope of making it seem to the visitors that they have never left home. But while we're all busy trying to be ersatz Britons for the duration of the royal visit, nobody is doing anything to help the visitors deal with America -- an oversight I hereby address.

An American diner holds his fork in his left hand and his knife in the right while cutting off bite-size pieces of food. But then he puts the knife down and transfers the fork to the right hand to put the food in his mouth. (We also use napkins and have our salads at the beginning of the meal.)

This is not to say that the British way of keeping the fork, upside-down, in the left hand (using the knife to mash mouthfuls of food onto it) is wrong. We just do it differently, that's all.

After all, you wouldn't use chopsticks to eat Ethiopian wat, or your bare hands to tackle Italian linguini. A gracious guest tries to do it the way the natives do it.

Her Royal Highness should not be upset if someone at a cocktail party approaches her with, ". . . and what do you do?" That is a standard conversational gambit for Washington party goers who typically haven't met each other before winding up at the same party. True, everybody at the party will know that the princess is there, but one or two might not know precisely which one she is. That's nothing to get offended about, and it is well to have ready an answer that is both helpful and gracious, like nodding toward the Prince and murmuring, "I'm with him."

The couple should be warned that any American with whom they strike up an amiable conversation is likely to suggest that they "have lunch sometime." This is not a situation that requires consulting one's social secretary, since no real invitation is involved. It is simply a way of saying, "I've enjoyed our chat," and the proper response is, "Yes, yes," followed by a quick smile.

In the event the royal guests stray from the official tour, they should understand that conversational gambits and compliments sometimes come in unfamiliar phrases. "What it IS," for instance, is not a question and means no more than "Hello." If they want to show that they have boned up for the trip, they might try responding, "Everything is everything," but that really isn't necessary.

Also, "That's a bad hat you got on" is neither a criticism nor an impertinence, and requires only a "Thank you" in response. And that is "Thank you," not "ta," which will only lead to confusion.

There's a good deal more I could point out, but it's almost certainly pointless to do so. Americans, who seem to think everybody else's culture is superior to their own, will go out of their way to avoid confronting the royal visitors with anything American.

Oh, well, nobody ever died of Brussels sprouts.