Bird calls. Shrieking sirens. Keening violins. And then, at 12:45 yesterday, a striking figure appeared on the roof of the National Theatre -- a man draped in cream-colored jersey, his head shaven, his back ramrod straight. He held a massive conch shell in his hands. Assuming the first of a series of sculptural poses, he blew into the shell as if to summon forth some mystical force.

His call was answered. Moments later, two smooth white heads surfaced slowly on either side of him, followed by four sets of chalky white hands. And then there they stood in their otherworldly entirety, a quartet wearing nothing but G-strings, their muscular bodies coated with alabaster body paint. Extending their arms, flexing their crimson fingertips, these four Zeuses looked out over their granite Mount Olympus, transforming the startled lunch-goers below into a hushed mass.

They crouched in unison, fastened rings to their ankles, ropes to the rings, tipped upside down and lowered themselves gradually into space.

Sankai Juku had arrived. The Japanese troupe, which gives new meaning to the term avant-garde, has staged many such "hangings" worldwide and was one of the unqualified hits at last summer's Olympic Arts Festival. Yesterday's event was sponsored by District Curators and Mitsubishi Motors as a prelude to the troupe's appearances this weekend at the Warner Theatre.

"We are part of a movement called Buto," declared Ushio Amagatsu, the troupe's director, choreographer, and conch-blower, at a press conference following the demonstration. "Sankai Juku is the third generation of that art form, which began in l960 . . . After the war, it was clear that there were cultural and physical differences that had to be recognized. Buto seeks to develop a greater sense of human understanding, and to further explore the origin of life." Sankai Juku, loosely translated as "mountains-water-school," has been influenced by the classical forms of Kabuki and Noh theater, as well as western modern dance and classical ballet.

The spectators at yesterday's "hanging," some of whom had come prepared for the bizarre exercise, gasped and surged forward at the first sight of the folded-up bodies dangling freely in space. A hundred cameras clicked. Swiveling at the ends of those ever-lengthening ropes, the performers seemed to metamorphose into sacks of bleached laundry, baby opossums, fetuses. Gradually they unfurled. The men gestured then, weaving their fingers about in some private sign language, flapping their arms like prehistoric birds.

About two-thirds of the way down, the quartet's movements grew more contorted. Curling their heads and chests into their torsos, they thrashed and flailed like trapped animals, or the inhabitants of some oppressive womb. And when they finally touched the ground, the crowd's relief was almost palpable. The performers, unperturbed by their rapidly encroaching fans, went about their ritualistic business, merging into a swerving collective, and ending with a ceremonious backward glide through the open doors of the National.

At the press conference inside the theater, Amagatsu , a small, fashionably garbed fellow with a shy smile, answered questions with the help of three interpreters.

When pressed to interpret the work that had just been performed, he demurred. "Every individual will interpret what they feel and see differently," he said, and went on to introduce the four other members of Sankai Juku.

Each offered his own greeting or commentary.

"As a result of the good weather today, I was enjoying my experience especially," remarked Goro Namerikawa.

Is hanging upside down beneficial to one's health? asked one reporter.

"Yes, it is very good for your health," repled Namerikawa. "I suggest that everyone try it."