An elite little street with the best cotton shirts in London

Only a short stroll from the tumult of Piccadilly Circus lies a quiet street that has tempted, teased, and attracted me ever since I made its acquaintance sometime back in the Mary Quant era.

Not every American visitor, nor every Briton, knows of Jermyn Street, which tucks itself away in London's West End between St. James and the Haymarket, selling quality merchandise from hats to shoes, cheese to bacon, antique books to plum pudding, but most notably the choicest cotton shirts any man (or woman) ever buttoned down.

Change comes slowly to this slightly aloof and elite little street, so I was surprised on my last visit to note the arrival of some trendy Italian-style clothiers and the formation of a merchants association. It was time, a Jermyn Street Association member told me, by way of explaining the group's nascence, that Britain and the world learned more about this rather too well-kept secret. Indeed a street fair had been so successfully introduced in 1981, with strolling minstrels and craftmaking exhibitions, that a repeat was scheduled for the first two weeks of this September.

I don't want to tempt you with the rich details of Jermyn Street shirt buying (for this will be the subject of a later column), except to say I found Turnbull & Asser, Hilditch & Key, Harvie & Hudson, and a handful of others so alive and well they were quoting eight-week waits per order at anywhere from $:30 to $:45 a shirt.

Jermyn Street doesn't really begin to bustle (if bustle isn't too forceful a word) until mid-morning, but that doesn't mean you shouldn't start your prowl earlier. Breakfast can be had at the Fortnum Fountain on the Jermyn Street side of Fortnum & Mason, the ancient purveyors of exotic foods. On the fountain door is a sign, ''Sorry no dogs unless carried.''

Perhaps the earliest bird on the block is Paxton & Whitfield, cheesemongers, at No. 93. In the window are Stiltons the size of washpails and 60-pound wheels of Cheddar; inside, above sawdust-covered floors, hang 15-pound York and Brodenham hams. Behind the counters wait blue-smocked clerks, who each have a year and a half of cheese-serving education, and more than 200 varieties of cheese.

On this November morning a customer with a German accent eschews the cheeses and picks from the counter a slab of English Wiltshire Streaky Bacon, as pretty as red marble. ''Is it to travel by plane?'' asks the clerk. Told it is, he declares, ''Then I'll wrap it in film.''

In the cramped back room, general manager Philip Rippon tells me: ''We don't use any refrigeration, and that goes for cheese as well as bacon, which we smoke and cure on the premises. We simply don't believe in chilling cheese. If you want to have some for lunch, it would never be ready in time.'' He said Paxton's carries 30 different English cheeses. ''When English cheese is good, it's the best,'' he pronounced.

Almost next door, at No. 89, is a shop of a different smell. Floris, dispensers of exotic fragrances since 1730, is like a sparkling jewel box. Its mirrored, paneled Spanish mahogany walls came to Floris intact from the Great Exhibition in Hyde Park in 1851. So says Dominic Browne, one of a half-dozen salespersons ready to please and inform. ''Our bath essences and toilet waters are very popular,'' he says, ''and among them this one is a classic.'' He anointed me with Special 27, a blend of cologne and red rose.

On the wall is a letter from Florence Nightingale dated 1863, thanking Mr. Floris for a nosegay he had sent her. And an 1871 entry book shows that Queen Victoria bought a hand cream for 7 shillings. Floris also carries such accessories as ivory hair combs and brushes, tortoise-shell combs, badger-bristle shaving brushes. Whether you pay $3.75 for a lavender sachet or $ 500 for a super badger brush, your change is handed back on a velvet-covered, well-fingered, wood tray.

One of my favorite Jermyn Street hideaways is John Faustus, at No. 94. For sale behind the pretty, small-paned windows are antiquarian books and master paintings and prints from the Dutch and Flemish schools. ''We're really no longer a book shop,'' says Susan Hadida, the owner, ''but we don't like to get rid of our books because they bring people in who would be scared off by art.'' On the wall are three Rembrandts. On the carpeted floor, asleep, is the owner's Cumberland cur, Kip.

You can eat reasonably well on Jermyn Street - a light lunch at Simpsons (the clothing and department store that is noted throughout the empire for having invented self-supporting trousers - no belts, no braces - in the 1930s); or lunch, dinner, and after-theater supper at Rowley's, a Paris-style bistro that serves only sliced entrecote, salad, and fries.

It is even possible to sleep on Jermyn Street. The 250-room Cavendish, at Jermyn and Duke, is on the very spot where Rosa Lewis, the ''Duchess of Duke Street,'' ran the original Cavendish. The present building, which went up in the 1960s, harks back to more illustrious days with various drawings, menus, and photos Rosa Lewis left behind. Not too much else, I am happy to say, has changed in her old neighborhood.