In the toughest turf in town, the runways set up in the courtyards of the Louvre, the Japanese have proved their inventiveness in fashion design to be no less formidable than their talent for computers and cars.

Japanese designers have fired the opening shots in the battle for fashion preeminence (and dollars) next spring. Shows by more than 50 designers will be held in the next five days; but the Japanese already may have conquered the Paris fashion scene.

Rei Kawakubo, who calls her company "Comme des Garc,ons," and Yohji Yamamoto were among the first of 10 Japanese designers whose offerings will be sent down the runway to be viewed by buyers and fashion press from around the world. Though some of the fashion crowd had not yet arrived from the shows in Milan and London, many of those who made it to the first of these shows felt it was worth the effort to reach Paris early and slosh through the rain and mud to sit in the cold tents.

"It shows us a whole new wave of dressing," said Vogue magazine's Polly Mellen, as she raced back to congratulate Yamamoto after his show. "It is modern and free. It has given my eyes something new and has made this first day incredible. Yamamoto and Kawakubo are showing the way to a whole new way of beauty."

The fashions, made in intriguing Japanese textures and weaves, are always oversized to the point that one size fits all. Kawakubo takes six months to develop a design. Clean, angular shapes and neutral colors, particularly black and beige, dominate the Japanese look. "They create an electric mix of neutrals and textural and tonal effects that are incredible," said Bernie Ozer, vice president of Associated Merchandising Corp., the world's largest buying office. He called Yamamoto "the Japanese Armani."

The Japanese are hardly new to the Paris fashion scene. Issey Miyake has been showing his innovative styles in Paris for almost 15 years, and Kenzo and Kansai Yamamoto (no relation to Yohji) have been among the heavy hitters here for several years now. And Hanae Mori, whose style is decidedly more Western than the others, has a successful couture house as well as boutiques in Paris.

The Japanese also are important buyers here. Tokyo-based stores send as many as 30 buyers each to choose the designs of the French that sell well in Japan. In many instances, the Japanese stores purchase more French fashion than the American stores. And banked against the runway for the shows are an increasing number of Japanese photographers recording the styles for Japanese fashion magazines.

Many of the French are not wildly happy about the Japanese intrusion on their fashion turf. "We had a struggle to get the French to give us tickets to the Japanese designer shows," said Benita Downing of Neiman-Marcus, who calls the Japanese designers "the group to watch."

Of course, there were dissenting views. Many in the fashion crowd were not enchanted with this new wave of design that undoubtedly develops from designers who are not locked into the Western traditions of dress and are willing to experiment with new cuts and shapes and textile technology.

While some found the Japanese easy-fit clothes free and comfortable, others viewed them as baggy and stretched out. And while many admired the carefree, crushed fabrics, others saw them as crumpled and messy. What, on the one hand, was light and layered with patchwork geometric cuts and uneven hems seemed, on the other, closer to the bag-lady look and punk than an agreeable new fashion.

"They are modern clothes for women today, like myself, who need to dress easily and quickly with uncomplicated style and not worry about being perfectly dressed," said Jean Rosenberg of Henri Bendel, who was wearing an outfit from Comme des Garc,ons. She described the Japanese styles as being as innovative and influential a change in fashion as French designer Sonia Rykiel's sweaters of 10 years ago.

Marjorie Deane, chairman of Tobe Associates Inc., an internationally respected fashion consulting firm, sees the influence as revolutionary as Courre ges' space-age styles in the 1960s or Karl Lagerfeld's recent fitted silhouette. "It is audacious and is sure to be misunderstood, but it is the newest direction in fashion," said Deane, who has been tracking fashion changes for more than 30 years. "It is the wave of the future."

Unfortunately, the Japanese have borrowed some of the old ways of the European designers--starting shows late and exaggerating some of the looks for the sake of the runway. Kawakubo, who doesn't like makeup at all, sent her pale-faced models down the runway with red splotches over their eyes and mouths, making them look too much like battered women. And Yohji Yamamoto opted for a white geometric painted face similar to the look of Kabuki actors.

Still, immediately after the Japanese shows many of the store buyers raced to the boutique of Comme des Garc,ons to study and purchase the Japanese styles. Said Bernie Ozer as he watched the buyer reaction, "Isn't it nice that you can finally weigh more than 10 pounds and look gorgeous?"