From butterflies to brash and black.

FOUR distinct generations of Japanese designers share the fashion stage in this capital city. For the most part, each generation has turned away from those that preceded it to make a unique fashion statement, while the previous generations of designers have continued to flourish. And all jostle with Western designers for a portion of the market. First generation In the 1950s, the designers of note were Jun Ashida, couturier to Japan's imperial women and other high-society doyennes, and Hanae Mori. Hanae Mori began as a costume designer for films, but her popularity surged after she showed her collection in Europe; her butterfly collection was lauded by many, including the late Princess Grace of Monaco.

Hanae Mori, a promoter of Tokyo as an up-and-coming fashion capital, has dominated Japan's high-fashion scene ever since.

The 1950s saw an insatiable market for women's ready-to-wear which ushered Ashida and Hanae Mori to the bank doors.

While these designers clearly have petite, dark-haired women in mind and frequently incorporate distinctively Japanese shades and textiles into their patterns, the styling of their fashions has always been and remains firmly Western. Next, brash designs

Japan's second-generation design coterie burst onto the international fashion scene in the mid-to-late 1960s. Many, like Issey Miyake and Kenzo Takada, sprang from that already established fashion center -- Paris. Together with Kansai Yamamoto, these designers created brash fashions that used traditional Japanese fabrics and styles. They borrowed from Japan's unchanging working-people's wear, kimono forms, and other wrap-around styles, and saw the body shape as basically flat and square.

The second generation's ethnic look and East-West blends emphasized design for its own sake, and the results, while always interesting, were not always wearable. (In 1983, in fact, a smattering of Miyake's fashions found their way into an exhibition of structural designs, organized by the Massachusetts Institute of Technology in Cambridge.) Variations in black

Third-generation designers arose during a considerably more affluent period than that of the preceeding two groups, and many are graduates of Tokyo's Bunka College of Fashion, a prominent Japanese design school. Yohji Yamamoto is perhaps the foremost among the early design-school graduates, while others, like Rei Kuwakubo, who eschewed formal training and instead earned her degree in philosophy from Keio University, chose to develop their creativity alone. Kuwakubo, to this day, claims not to be able to

sew.

Yohji Yamamoto and Kuwakubo are the designers who first saw limitless variations in black, and introduced it to the international runways as blue-black, greenish-black, and shimmering black with, perhaps, a touch of gray thrown in for color and contrast.

Asked, ``Why black?'' Kuwakubo, now head of the 18-year-old (and very successful) ``Comme des Garons'' line, said simply, ``There is too much color in my life.'' She was dressed somberly in black, without makeup.

Yohji Yamamoto, an impish looking man, explained that his widowed mother dressed severely and that, in his youth, he learned to delight in the profound variations he could see in dark monochromes.

Recently, with international criticism heating up about the Japanese ``black bag'' fashions, both designers have begun to incorporate dashes of red, purple, white -- color -- into their collections.

Other criticisms of Japanese designers in general have surfaced in response to recent shows. Despite the fact that these designers were touted in the early 1980s as among the freshest and most innovative, comments of late have included such remarks as ``nothing new'' and even ``unwearable.'' Now where? -- the fourth generation

Where is Japanese fashion going?

Tokyo is now firmly on the fashion map, and designers say it is easier to break into the business. The back streets of Omote-Sando and Harajuku, trendy sections of western Tokyo, are spotted with small design studios.

The faades change with discomforting frequency, however, and there is no distinctive theme tying the young designers together, except perhaps the use of lots of color and unconventional materials, and the fact that the clothes no longer ``look'' Japanese.

Older designers say the biggest challenge facing the fourth generation is that Japanese consumers aren't as daring as they once were, and almost 95 percent of the buyers of Japanese designs are Japanese in Japan. Unmarried women are expected to spend lavishly on their wardrobes, but that freedom often ends abruptly when they get married. Preppy is popular

Western fashions have been in Japan for just a century and have been worn by the majority of the people only since World War II. Therefore, the Japanese still sometimes see Western clothes as a bit of a costume.

An office worker, instead of having her own ``look,'' may dress ``punk'' on Friday night; in black, baggy clothes Saturday afternoon; ``preppy'' for Saturday night; and in bows, frills, and ruffles for her friend's party on Sunday evening.

For everyday wear, conservative ``preppy'' clothes are by far the most popular, although they're still seen as somewhat of a costume.

The Japanese are nearly tweedier than the British these days, and Brooks Brothers, Paul Stuart, L. L. Bean, Eddie Bauer, and Ralph Lauren all have a presence here, despite their astronomical prices.

In Japan, where anything goes, the Japanese are going button-down.