The Kabuki actor struts rakishly across the stage, wearing an elegant band of purple silk around his head and gesturing with a gold-colored fan in the decadent ways of the classical Japanese dandy.

As the Japanese stringed instruments twanging away in the background race toward a climax, Shoji Mori, an elderly gentleman seated in the far balcony, suddenly jumps to his feet and bellows: "You sexy devil, you." Mori, 81 and a spritely great-grandfather, has spent the better part of the last 66 years hurling verbal zingers at the stage of the Kabukiza, Tokyo's oldest playhouse for Japan's traditional theater, to the delight of its actor and patrons alike. The Grand Kabuki troupe, now on an American tour, will bring its special brand of theater to the Kennedy Center for seven performances beginning Tuesday.

Mori, who will not make the trip because of the expense, is the senior member of an exclusive band of Kabuki buffs who come to the Kabukiza daily to shout the praises of their favorite players in a guttural style that, to the foreign ear, may sound more like a primordial grunt better reserved for a wrestling match than an expression of high artistic appreciation.

The play this particular day is a famous dance number based on a purely Japanese historical theme. It deals with a young man-about-town whose lover, the narrator intones, has evaporated like the morning dew. As if on Mori's verbal cue, the actor, one of a long line of hereditary Kabuki superstars, cocks his head in an ostentatious pose and heaves a sigh of apparent grief.

Here the act ends and a flurry of approving shouts in throaty Japanese erupts from other men in the audience: "You're the greatest," ". . . Tops in your generation," ". . . The spitting image of your grandfather the actor ."

Called Omuko-San (literally, "Mr. Great Beyond" in Japanese) after the seats they frequent in the uppermost gallery--the cheapest in the house--they are generally regarded by other theatergoers as a living link with Kabuki's colorful, plebian past.

Kabuki, it is said, developed about 400 years ago from impromptu, often ribald plays put on by itinerant actors for the common man on the banks of the Kamo River in the ancient capital of Kyoto.

Early actors and actresses moonlighted by selling, among other things, sexual favors. This prompted a 17th-century shogun to ban women from the Kabuki stage where, today, all roles, including female ones, are played by men.

Subsequent centuries, and generations of well-heeled patrons, brought great refinement and respectability to the Kabuki stage, but it still retains some of the popular flourishes that made the theater a symbol of the radical chic of Japan's feudal days.

Mori, a retired house painter, says it is the flamboyant acting styles, gaudy costumes and the pageantry of the stage that got him hooked when a group of friends persuaded him to attend his first performance in 1916.

But he suggests it is the intricate plots that dwell on events in Japanese history, the valor of the samurai warriors and the pathos of star-crossed love affairs between men and women from the wrong side of the tracks that has kept him coming back for more.

"In those days," he said recently, "there were lots of small Kabuki theaters in Tokyo and I thought the shouting from the audience was simply great. I don't know when or how it happened, but at some point I just started to stand up and yell, too."

Today, Mori's repetoire ranges from simply intoning the Japanese equivalent of the actor's stage name to bolder exhortations and even comic rejoinders to actors' gestures or speech. All of these verbal antics are intended to inspire the actor to greater heights and the shouting of a well-timed word or phrase can, Mori asserts, help coach the audience in the finer points of a play by indicating where and when to laugh, cry or applaud. "It's not like shouting at a baseball game," insists Ronald Cavaye, one foreign Kabuki enthusiast, "and it's more than the simple equivalent of applause. When it's well done, it's certainly a minor art form because of the precision timing involved" and the sense of audience participation it provides throughout a play.

"Many tourists including Japanese are dreadfully surprised" by the staccato calls regularly coming from the upper galleries, he says, "and spend as much time craning their necks trying to glimpse one of the shouters as they do looking at what's happening on stage."

"We hold the real behind-the-scenes power in Kabuki," says Keisuke Mizutani, 58, "because by shouting we heighten the effect of the play . . . If you misjudge the timing by just a split-second, you can ruin the actor's concentration and hurt rather than help him."

That is why, Cavaye says, they tend to take a dim view of people they consider interlopers. They take exception to people who shout more for their own pleasure than the actors' benefit. But the temptation to join in, he admits, can sometimes be hard to resist, as it has been in his own case. "After all, it's rather nice to stand up in a theater and shout."

At the Kabukiza today there are three dozen or so Omuko-San regulars, although in recent years their numbers have been dwindling. As a result, the management has embarked on a campaign to protect them much as environmentalists would an endangered species of wildlife. They are, for instance, issued with lifetime free passes to all performances throughout the year.

On an average day, Mori spends about nine hours at the Kabukiza from the start of the late morning matinee to the end of the last evening performance. Most of the time you can see him perched on his seat in the balcony like a rare old bird.

He is watching a band of actors made up as kimono-clad samurai stroll regally down the hanamichi, the runway that connects the back of the Kabuki theater with the stage and on which some of the key action takes place.

On his feet now, Mori dreamily mimics the actors' facial gestures and repeats their lines softly to himself. Suddenly, his back arches, his elbows shoot back wing-like, and he crows:"Geeyuuuuuuuu sheecheeeeeeee dieeeeee-maaaaay!" (the phrase, in Japanese, means "17th generation" and Mori intends it as a compliment to the lead actor, who is 17th in a long line of state greats).

Not unlike members of claques in Western opera, the Omuko-San are courted by famous actors to ensure that the kudos keep coming. They may receive small gifts of money or sake each month or expensive items such as formal silk kimonos bearing the actor's family crest.

Among the more than 200 extant Kabuki plays, one of Mori's favorites is the dance drama "Masakado." The play, set on a gloomy, rainswept night, tells of the warrior Mitsukuni's visit to the rebel general Masakado's ruined palace to check on rumors that Masakado's heir is plotting insurrection.

Eerily, Masakado, an evil sorcerer, appears in the guise of a beautiful courtesan geisha and, failing to seduce Mitsukuni to his doom, confronts him with her magical powers. The ramshackle palace collapses, and the entire edifice sinks to the stage floor in one of the more spectacular special effects of Kabuki theater.

American audiences will soon have a chance to see Mori's favorite play firsthand, as it is one of the centerpieces of the tour.

Utaemon, Kabuki's leading female impersonator, will headline the cast along with Kanzaburo, who is perhaps the theater's best-known male lead. Both men have been designated by the Japanese government as "living national cultural treasures."

Although Omuko-San will be missing, Mori says he expects off-duty Kabuki actors will take a stab at shouting at their counterparts on stage, to put the finishing touches on the authentic atmosphere the program's producers are planning to create.

Says Mori with a grin, "I'd love to try yelling in an American theater. People might be surprised, but I wouldn't care."