PARIS, MILAN, LONDON; European spring showings mirror the mood of the times

Waistlines have been dropped more than once. Skirts and trousers were often shortened to astonishingly high levels. Suede garments, thought to be for cool rather than warm climates, emerged as bona fide spring and summer high fashion.

At the time, such occurrences on the European fashion circuit - starting in Milan, continued in London, then Paris - seemed eventful. Yet what lingers in the mind after last month's round of advance ready-to-wear showings has less to do with unusual materials, altered shapes, or shifting beltlines than with changes in perspectives. In retrospect, the most significant feature of the recent openings was the way they mirrored reactions to the times in each of the three stylish capitals.

As always, the new fashions had certain common denominators. Among the recurring themes on the runways were dramatic playoffs of black against white - sometimes through mixes of plaids, stripes, and polka dots, or of companionable prints, a melange favored by Emmanuel Ungaro in Paris.

In contrast, there were masses of vibrant color, beginning in Milan with Giorgio Armani's brilliant plain and patterned combinations of vermillion, turquoise, chrome yellow, and billiard green. Although the Italian designer's new short and boxy silhouette, sashed low on the hips, suits only the young and lissome, his color palette has universal application. Elsewhere, striking rugby and gay carnival stripes prevailed.

The French, whose socialist government is having a dampening effect on buoyant spirits, nonetheless took a playful, insouciant stance with clothes that were mostly full, exceedingly short, and generally colorful (although every collection included large amounts of unrelieved black). Some Paris designers who used their shows as platforms for political statements presented black in the form of Iranian mullah or Sicilian widow outfits.

The born-in-America idea of separate pieces for all times of day turned up everywhere, even in the exquisitely beaded art-deco clothes at Versace. New ways of wearing components were suggested by light layerings of lengths-on-lengths - double skirts and aprons over pants, especially.

This kind of turnout was beautifully executed by Karl Lagerfeld for Chloe, the Paris pret-a-porter house, in spaced Matisselike prints of crepe de chine. Whether as abbreviated as his circular, floaty culottes or as lengthy as his below-calf dresses, nearly everything was firmly confined around the midriff with Lagerfeld's patent or boned-fabric corselet belts. They were the only archaic notes in an otherwise modern collection.

The low torso look, an alternative to the corseted midsection, was a newsy trend. The order to ''drop that waist'' and ''lower that belt'' appeared to have been well-circulated at many houses. The descent of the waistline was usually accompanied by an inflation of the blouson top

Far more luxurious in their approach than the French, the Italians produced a sportive yet highly polished brand of elegance that can be seen on the streets of Milan any day of the week. The Italians are all for trouser styles and the Milanese seem to be on a knickerbocker holiday. Young shop girls wear knee breeches with white (or flaming red) stockings and low-heeled pumps as they stroll around the Galleria with their dates. Whole families, including the children, cut bella figura decked out in tones of khaki, the smartest color of the year. Even the smallest child wears his (or her) fashionable touch of metallic trimming.

With this innate pride and perception of style, in combination with a fund of well-developed talent, it is not surprising that Milan is beginning to surpass Paris. Superior suedes - those by Armani for Mario Valentino were printed, woven , pleated, shirred, dyed in joyous colors, and fashioned into every conceivable shape - are works of art. They are also evidently easy to wear. Girls who modeled the lightweight unlined leathers under the hot lights at the showings found the suedes porous. Even under those conditions, they do not stick to the body, models reported.

Incomparable knits, another area of Italian preeminence, were as top-drawer as ever. The Missonis pepped up their sweater dressing with miniheight circle skirts over cropped-length bicycle pants. Mariuccia Mandelli of Krizia showed only a few of the animal-patterned sweaters for which she is famous. Instead she wove metallic threads imaginatively through irregularly striped sweaters.

Metallics rated high for spring in Milan and London; not so high in low-luxury-profile Paris.

Escape-dressing continues to flourish in London, a response perhaps to what residents there admit is, ''quite frankly, a recession.'' The far-out New Romantics who initiated Regency dandy clothes have decided to be less outrageous. Swashbuckling eye-patch pirate looks are being replaced. Vivienne Westwood, the Kings Road designer who put them on the fashion map, is bringing out a line of ''Robinson Crusoe'' torn suedes.

Excellent chamois and leather prairie skirts and blousy tops shown by Nigel Preston for Maxfield Parrish were a good deal simpler but nowhere near as spare of line and cut as the fine suedes at Jean Muir. She fashioned printed skins as well as plain and perforated kinds superbly into collarless coats and jackets with kimono sleeves.

Zandra Rhodes's inspired collection of fantasy evening clothes came in pastel (powder blue or turquoise with shell pink) chiffon and organza or else dark-grounded prints - all with the tattered or jester-pointed hemlines and other individual touches she favors.

The Paris designers demonstrated their uneasiness under the socialist regime. Rumblings of the tumbrils were sometimes almost audible as garments with French Revolutionary overtones came out. Among them were the Phrygian bonnet at Michael Goma, the Marianne outfits (right off the French postage stamp) with Tricolor cockades at Claude Montana, and the three matte jersey dresses of red, white, and blue that formed the finale at Saint Laurent.

Talk of a return to the ''poor look'' instituted by Coco Chanel in the long-gone '20s was in the air. Givenchy and Chanel, whose customers include some of the world's richest women, shortened skirts but generally stayed with quiet elegance. Yves Saint Laurent, the most reliable barometer of style directions in Paris, had only one gold kid blouson in his procession of clean-cut, spare-looking clothes. Many were of such plebian fabrics as poplin. He chose classic simplicity. Isn't that always the best way?