Paris in the spring

French ready-to-wear collections for spring and summer, presented here in mid-October, were rather like that little girl with the curl in the middle of her forehead. ''When they were good, they were very, very good, and when they were bad, they were horrid.'' Leaders included Yves Saint Laurent, perennially on top; Karl Lagerfeld of Chloe, who will take over as head couture designer at Chanel next January; and Claude Montana. Valentino and a handful of others were superb. This is more than can be said for many of the younger, jazzier houses that played up ''poor girl'' looks with rags and tatters quite worthy of the secondhand stalls at the Paris Flea Market.

Numberless themes, most of which are developed in a very wearable manner, were presented under the giant green-and-white-striped circus tents set up in the Cour Carre of the Louvre with all the panache and showmanship of a Broadway musical production. No one really expects the shows to start on time, but this season broke all records with presentations up to an hour and a half late, postponed at the last minute until a day or so later, or canceled completely.

But most of the fashions were worth waiting for - brimful with ideas and ways to revamp some of the clothes already hanging in our closets. As one French fashion expert sums up, ''Making a salient fashion selection has a lot in common with choosing the right man; a careful choice will see one through almost everything and does not necessitate constant replacement.''

We can all relax concerning the question of hemlines. Every length is viable, from skirts featured well above the knees to midcalf and ankle lengths often made of sheer, transparent fabrics for formal wear that silhouette the legs against the light or take on high slits up to the thighs. Pants tend to get the short end of it. A great way for an instant new look is to chop off last summer's trousers well above the ankle bones or shorten them to Bermuda lengths. These can be worn with loose floating shirt jackets or long blousons over bare-midriff suntops or bustiersm .

Saint Laurent scored constantly throughout his 160-piece collection, based on wonderfully colorful Carioca and samba dresses with flouncy skirts and peasant blouses, dramatic floral prints, or vivid, solid-toned primaries. His constant emphasis on separate pieces, even the town suits with long Edwardian jackets flaring out over the hips, provide many possibilities to stretch a limited wardrobe.

Two dominant trends at Saint Laurent are the revival of his star motifs, which he featured a few years ago, and the flower themes. Part of Yves' genius is his knack of readapting tried and true ideas such as a veritable constellation of stars in giant stylized effects on cotton prints and costume jewelry. He employs field flowers in charming, fresh ways. Life-size red poppies , daisies, and corn flowers speared with sprigs of wheat decorate jaunty straw boaters. They can be clipped in the hair or on one shoulder or tucked into wide-draped sashes. Even the bride is ecology-minded in her one-shouldered white cotton gown set off with a floral crown and ''bouquet'' of wheat sheaves.

Other themes in other collections evoke nautical influence. The fleet's in town and literally dressed for action in navy-and-white combos or flag colors featuring stripes of every width. There are pea jackets galore with shiny brass buttons and anchor appliques, Admiral's caps and US sailor hats, middy dresses, and ''dress white'' pant suits.

More bathing suits turn up on the high-fashion runways than ever before, including sleek, elasticized one-piece tank styles with legs cut up to the hipbones at each side. All sorts of coverups, terry cloth or jute togas, ponchos , and caftans go from the pool to patio or even a midnight beach party.

Many designers are on a fitness kick. Casual wear often traces its origins to gym togs, jogging suits, sweat shirts, and sailing gear. Formal clothes are either madly frivolous and romantic or evoke the old Hollywood vamps in clinging gowns with lots of elaborate embroidery. As Karl Lagerfeld, now the ''high C'' man for both Chloe and Chanel, sums up, ''Fashion without wit is disastrous.'' He proceeds to embroider life-size guitars or violins down the entire back or front of slinky black crepe evening gowns.