Not even a bomb scare on the final day of French ready-to-wear showings for fall could diminish buyers' high spirits and optimism over this week's fashions.

The threat came two hours before the Kenzo show. Students who had acted as ushers for the week-long showings were deputized to check every purse and every shopping bag brought into the tents in the garden of the Louvre. With great embarrassment, they perfunctorily peeked at each person's belongings, apologized for the intrusion and directed the buyers and press to their seats.

But despite the temporary disruption, French designers had good reason to be happy: Stores are leaving bigger-than-ever orders with many of the houses.

"It proves that nothing is forever--even bad," said Arnold Aronson, chairman of Saks Fifth Avenue, who expects to boost sluggish retailing business with these collections.

"In this business, hope springs eternal," he said. "Our purpose is to sell, and I think we will sell these clothes well."

What helps even more, perhaps, is that the clothes for fall have not been pushed to unwearable extremes. In an effort to sell more in tough economic times, designers have curbed the outrageous, cleaned up the contrived and enhanced the enduring classics with color and proportion.

The clothes are more spirited than they were during the last round of showings in Paris last October. Now the black dresses are sexy and brightened with dashes of color. Last time the music was punk rock. This time it was Charles Trenet and Edith Piaf. And last time, when Claude Montana wanted to show red, white and blue, it was paraded as a revolutionary uniform. This time the Montana bridal party that concluded his show wore red, white and blue, but the effect was a patriotic tricolor.

Even when Kenzo decided to put military accessories on his very commercial collection, the models carried bubble-gum pink and lime-green machine guns, and rifles were stuffed with flowers. He showed richly floral-printed, Russian-style dresses and Japanese- or Chinese-inspired outfits.

The wit carried over to other shows. Sonia Rykiel's models in golf sweaters used rhinestone-decorated golf clubs to hit Day-Glo tennis balls. Thierry Mugler's "secretaries," with French-twist hairstyles, wore pastel wool dresses and carried briefcases. His "thieves" wore tight black dresses with rhinestone collars, big bracelets and earrings. And Jean Claude de Luca's "Vassar girls," as he calls them, wore leather Spencer jackets and moire' taffeta pants, or pastel argyle knits with knit petticoats poking out from under the skirts. All amusing and all very wearable.

Several recurring themes make clear just what fashion ideas will trickle down from these showings. They include:

* Clothes that are big and roomy at the top, often because of dolman batwing sleeves. Dropped shoulders and a looser fit give an oversized mannish look to many of the coats and jackets.

* Black as the background color for many clothes for day and evening, with black and white a favorite for plaids, and bright color accents on black used everywhere.

* Lapels that seem to be getting bigger and sometimes extend to cape or poncho sleeves.

* Gloves, even gauntlets, and hats everywhere, most of them with big brims from sou'wester variety to boaters.

* And two old favorites that refuse to go away. The ruffle is still around, but now as a flat ruffle on a dress or cascading on a skirt. And the metallics are dull and diffused rather than shiny gold or bronze.

* Finally, hemlines are both long and short. Several designers have answered the problem with uneven hems. Valentino might have the best solution of anyone. He's done evening sweaters and blouses over short slim skirts that are cut on an angle to incorporate two lengths in one. Said Catherine di Montezemolo, vice president and director of fashion for Lord & Taylor: "The woman who buys a short skirt will probably also want one that's long. We are already selling both lengths."