London

You appear tiny, delicate, vulnerable in your huge man-tailored overcoat reaching nearly to your ankles. You sizzle in your satin party dress of sharpest cerise.

In between? In between you stride in a dashing herringbone tweed dandy jacket , velvet-collared, swinging sharply from a nipped waist and worn over matching tweed trousers that narrow in slightly Teddy boy-style toward the ankle.

That's your picture, your presentation, as the woman of English fashion, autumn 1984.

And if you drift into another mood, into that of the sassy, rebellious young, your midriff is on full display as you swish about in a crop top of graffiti-scribbled black wool, a miniskirt with turned-over waist, very high heels with almost winkle-picker toes. This alternative look is, in fact, bigger news than you'd at first guess, for as street fashion it riveted the store buyers from America and the Continent when they came to London's autumn fashion shows to see what's been termed the revival, the rebirth of British young fashion. The slinky show-all knit and jersey clothes of young trendsetters like Bodymap, which look right on about 1 percent of the population, are what seized the foreign attention.

But Britain's ''trad'' clothes are on an upsurge as well, with Daks registering a new tartan, quite formally, with Lord Lyon King of Arms (it's a navy with wine), and Burberry's rather unexpectedly bowing to London demand and lengthening its traditional tartan skirts. Both firms and others in their field show blouson jackets of fleecy loden with these tartans, often with tartan revers and/or linings, and silk blouses in the famous house checks are on the way too.

Men's suitings, in this highly androgynous season where every other garment is shown with a man's necktie casually knotted, are the winners. The dandyish velvet Chesterfield collar on your worsted suit recalls, all too vividly for some, the clothes of the 1950s.

But skirt lengths do not, for they creep ever longer, much longer than they were in the 1950s. Travel by bus and escalator may be fairly hazardous this coming winter, for the coat lengths, in particular, are down to four inches from the ground and you really must scoop up the hem as you move about town. Ace buy in the luxury stakes comes from two rival firms, Richard Shops and C&A, who both have huge man-tailored overcoats of this length in pale gray and cream, respectively, and of 75 percent cashmere, 25 percent wool, at exactly the same price: (STR)99 ($130).

Wallis Shops, too, loves the huge floor scraper, and theirs in sober blacks and browns reflects the mood of Sheridan Barnett, one of Britain's most creative designers, who dubbed his collection for autumn the ''Bloomsbury Look'' - which could be interpreted as understated chic or actual low-key dowdy, depending on how dashing the wearer. Mr. Barnett, teetering financially on his own, has now been offered a financial life belt by the big firm of Reldan.

Sober indeed the palette of London's ready-to-wear, brightened by a few sapphire blues at Marks & Spencer, a few garments in raspberry to cheer the taupes and pewters at Alexon. It was left to the high-style individual designers like Jean Muir to inject the sprightliness of bright colors like cerise in rayon jersey prints of whirling planets, and Wendy Dagworthy (a favorite of the young slouchy dressers) to cheer with shocking pink and sharp yellow.

Bob Schulz made a welcome return to the London scene after his years of designing for Italy's big chain group, Rinascente. He is delighting his old fans (from Jaeger design days) with the short skirts he, Saint Laurent, and Geoffrey Beene stand for - almost alone in the design world.

Cozy among all the rather severe tweeds, worsteds, and flannels symptomatic of this androgynous wave, are the mohairs in dark brown used in Roland Klein's huge coats. London designers did far less with dark browns than expected - in view of Italy's great passion for every brown from mushroom to bitter chocolate, not forgetting earth and rust tones. London is still showing lots of black, but taupe will edge it out as the season goes on. It looks chic paired with black, as in striped long cardigans in the Sonia Rykiel mood. Pine green at Janice Wainwright and Hardy Amies made a welcome comeback.

Hips are the focal point, and many a dress is swathed there (taking a cue from the satin maternity dresses of the Princess of Wales). The skirt of the season is long, lily-trumpeted at hem, snug over hip. Sweaters either continue cropped and floppy like this summer's or else are very long. Either way the pattern is a self-pattern, very strong, from Aryan fisherman types right on out. Ribbed diagonal collars are important. But the hip belt could be your wisest buy if pennies are scarce.

The long straight wool muffler, ideally in a stunning color like canary yellow or fuchsia, is the other must accessory, and it's seldom knotted, just worn plain round your neck, its ends flopping over your front. Bags are soft, unstructured, and heels are either high or quite flat.

Though clothes are indeed moving closer to the body, few as yet have that body-hugging, almost vamp quality shown by the Paris couturiers. So far that's reserved for the strapless satins and velvets of after-dark wear.