Extrawrd'nry!

Most sojourners in foreign lands are pleased to be taken for natives, and they often work quite hard at it. To be asked, say, on the streets of London by a man from Detroit (yourself being from Illinois but in tweeds) for directions to Paddington Station is bliss. To be able to give them without hesitation is very heaven.

On the other hand, nothing puts your average tourist off quite so much as finding out that he has got things mixed up - that even an eagle eye for, say, routine British civility has nevertheless run him into deportment that in native eyes lacks grace. But when it takes two encounters in one day to make the point, as it did for me several years ago in Cambridge, well, it's time to stay indoors - or better, in the instance at hand, to consult a bespoke tailor. For the culprit in my faux pas was - I tremble to confess it! - a cap.

It was just an ordinary English cap with a button on the bill, neither so wide and slouched as to suggest that of a cabbie nor so narrowly neat as to be trendy. I was particularly attached to it because it had been made to match my tweed jacket, making, I felt, a rather jaunty outfit. Was there any reason not to wear it on an excursion from Cambridge down to London? Of course not. So I rolled my umbrella tightly, set my cap at just the right angle, and off we went, my wife and I, on the 08:58 for London.

''You wore that cap to London?'' exclaimed the Master of my college when I later told him about my adventures. ''Extrawrd'nry!'' - but that's getting ahead of the story.

The first hint that something or other had gone wrong in the big city came as we were rising from lunch at The Bull and Mouth, one of those amiable pubs near the British Museum. My umbrella and cap, resting on the ledge behind the triangular corner booth during a lunch of pork pasties, had fallen over the rear edge and had to be retrieved by the waiter. He handed me my umbrella and then, rather hesitatingly, the cap.

''Is this your cap, sir?'' he ventured.

''Yes,'' I said, hearing his italics, to be sure, but not quite knowing what to make of them. ''Thank you very much,'' I added, forgetting that the British often use this phrase when they are a bit nettled.

As we picked our way through the crowded tables to the door, I felt the waiter's gaze fixed on my back, and I more than fancied that I heard, faintly but unmistakably, the word, ''Extrawrd'nry!'' spoken aside to another patron.

This appraisal lingered but troubled us only briefly: After all, it was only the first hint. The treasures of Tutankhamen's tomb awaited us in the British Museum. So I tugged my cap into place, tightened the roll of my umbrella, and around the corner we went, where, after two hours, we entered the great maw of the B.M., and so the rest of the afternoon to ancient Egypt - momentarily on Great Russell Street, W.C.1.

But hint No. 2, which was somewhat clearer, awaited us on the train ride back to Cambridge at the end of the afternoon.

The 17:36 to Cambridge from Liverpool Station stops first at Bishop's Stortford and then at Audley End, conveying to nearby fashionable Saffron Walden numerous London business executives who commute the 40 miles daily, carrying briefcases, tightly rolled umbrellas, and wearing, alas, no hats of any kind. My wife and I sat opposite two of them at a sort of card table between the seats, my umbrella (now really tightly rolled) and my cap carefully stowed in the overhead rack, along with their cases and umbrellas.

The ensuing conversation was very genial, establishing among other things that they both worked at Barclay's Bank in London and that I was an American professor working for the year in Cambridge.

At Audley End, 20 minutes before Cambridge, our fellow passengers bid us a pleasant good evening and stood up to reach their cases and umbrellas from the overhead rack. One of them unintentionally knocked my cap to the aisle floor. My wife reached to retrieve it, but one of the businessmen politely picked it up first, appearing to regard it with some curiosity.

''Is this your husband's cap?'' came the question, with more than a faint air of disbelief - and with italics again, you understand.

''Yes,'' my wife replied, ''thank you very much.''

Suddenly the image of the pub waiter rose in my mind, so I was not really surprised to hear one fellow passenger, as he stepped from the train, utter to his companion, faintly but unmistakably, the baleful word: ''Extrawrd'nry!' ''

The train started up ever so slowly and smoothly, and through the window I watched the two retreating into the twilight of Audley End, engaged in animated conversation - almost certainly about my cap. We still had 15 miles to go, and we rode them out in vaguely troubled silence.

''It might do for a weekend in the country,'' the Master explained next day, ''but no gentleman of parts would ever wear that cap to London.''

''Thank you very much,'' I replied, hearing the italics yet once more.

But I ''took his point,'' as the British say, and thereafter always went bareheaded to London.

As for my dear cap, I hung it on a peg in the rear of a closet and waited patiently for someone to ask me for a weekend in the country. But no one ever did.