Dresses sweet with sentiment

So sugary-sweet are this spring's English clothes, you almost should suck a lemon drop while shopping. The sugared-almond colors rule - every other dress is baby blue, lemon yellow, pistachio, face-powder pink, perhaps a clear coral.

The styling tends, on the whole, toward gentle nostalgia as well. The sugary colors are this year's sentimental substitute for last year's Princess of Wales frills, and it's rather a relief to report that the frills are now taking a holiday. The dresses, though, are the sort you wear to meet a future mother-in-law: demure white Peter Pan collars (very Chanel, this, even to the fake white, pinned-on camellia) with long-torso bodies and a hip seam from which spring flat pleats. If the dress is specially trendy, it will have dolman sleeves.

London designers are tired, on the whole, of the pouf Edwardian sleeve popularized by the Princess. The irony is: Parisian couture still loves it, showing it everywhere in the January collections for $1,000-a-suit customers.

The alternative to all this sugar-sweet dressing is the untamed hessian look, with slash-neck dresses of hopsack girdled round and round with real rope. Their skirts are wide, often patch-pocketed, and if they're not long enough in themselves for the window-dresser's taste, she slips a longer cotton skirt underneath. The look has dash, especially when shown with a twist-crinkle cotton-crepe scarf at the neck, a batch of raffia bracelets at the wrist, and the new sheer-color tights rather than the ribbed ones popular in winter.

Among other directions you can take if pastels are not your dish, is the strictly tailored suit in black and white, often chalk-striped or dice-checked, neatly belted with a peplum frill and a slim skirt. Or, consider the whole wave of Japanese work wear - inspired by those offbeat Tokyo designers who made such news in Paris last season. They used such quietly strong mixtures as navy with gray, black with cream, and they have been copied in mood by such lively fashion chains as Warehouse, whose designer Jeff Banks makes separates in these sturdy cottons.

Sheridan Barnett was another of Britain's name designers who felt inspired by the work-wear wave. In his group of long, slim smock dresses and tabards, there was only one bright color in the lot, coral.

The loose, somber look comes from another influence, too - a cooperative of young designers called Notre Dame X says its new clothes are inspired by the American hobo look.

Linen, which has captivated Ralph Lauren and Calvin Klein in America, is much loved in London, too. Jean Muir did beautiful circular midiskirts in it; Janice Wainwright, a series of striped separates that is quite new for her. Most effective for those who dislike ironing the stuff is the stream of linen knits. Crunchy cottons are popular at all levels, from Taiwan machine knits to couture-level hand-knits.

Skirts are at every possible level, from pelmet minis to long, stitched-pleat ''golfing'' skirts that nearly reach the ankles. But most clothes, slimmer than last year, are a couple of inches longer as well. While blouson jackets continue , the newer suits have snug, short-fitted jackets or long, unlined shirtlike ones.

The '50s influence, triggered by exhibitions at the Victoria and Albert Museum and at Liberty's, takes the ''Grease'' revival form of strapless tops, tight denim pedal pushers, neon-bright plastic jewelry, and whirling long skirts as well as the calmer side of the '50s, with its padded shoulders and tight-waist tailoring. But it's not overwhelming so far - most shops report that their customers like the '30s more than the '50s in fashion styling and are buying up those aforementioned demure dresses with their hip seams and tucked crepe bodices and gentle airs.