The koto and the shakuhachi, the two most important instruments of Japan's traditional music, have remained essentially unchanged for centuries, perhaps because their roots are so deep and strong, perhaps because they have reached a kind of perfection. Western instruments of comparable vintage -- the lute and recorder, let us say -- suffered centuries of eclipse and have been revived in modern times, but their function in our musical life today seems different from that of the koto (an intricate structure of plucked strings) or the shakuhachi in Japanese musical culture.

That difference was illustrated Wednesday night at the Kennedy Center Terrace Theater in a fascinating "Music From Japan" concert by two consummate musicians: Hozan Yamamoto, shakuhachi, and Tadao Sawai, koto, samisen and voice. Both are composers as well as performers, and that may be a key to the special role of their instruments in music today.

The Western lute and recorder have been revived essentially in a mood of historic piety; they are busy again playing the music of the past but, with a few eccentric exceptions, no new music is being composed for them. The koto and shakuhachi, in contrast, are part of a tradition that is still living and developing; four of the six works on the program were composed in the past 12 years. There are modern elements in this music: use of a taped soundtrack with the shakuhachi in Yamamoto's "Chikukyu Zanmai" ("Three Colors of Bamboo"); radical ways of hitting or plucking the koto strings in Sawai's exquisite little tone poem "On the Wings." But there is also a clear sense of continuity with the instruments' great tradition; it is, unlike much of the modernism in Western music, a modernism with roots.

The contemporary works felt at home in a program that included "Kogetsucho," a work from 1903, and "Zangetsu" ("The Moon Left in the Morning Sky"), from 1800. Throughout the program, the subtlety of nuances in dynamics, pitch and shadings of tonal color was extraordinary; the koto produces marvels of multilayered sound texture; the shakuhachi has an extraordinary resemblance to the human voice and a great variety of tone, including some of deep, expressive warmth. This versatility is, of course, a tribute to the players as much as the instruments.