"One of my earliest fantasies was to make something with light that had a physical presence, something that people could walk through. The dancers are realizing that fantasy for me."

Laser artist Rockne Krebs sits in his U Street loft, puffing on his umpteenth cigarette of the day, musing about "Laser Dance." This ambitious, evening-length work -- a collaboration by Krebs, choreographer Maida Withers and composer Bob Boilen -- will have its premiere Thursday and Friday at Lisner Auditorium, but Krebs is still busy fine-tuning his ultratech end of things. Charts and blueprints of intricate laser patterns cover the walls and drawing tables. On paper they look like so many blue-penciled zigzags.

"Would you like to see the laser?" Krebs asks, as if reading a visitor's mind. It turns out to be a long cylinder of a machine, water-cooled, thoroughly unglamorous. But then Krebs turns it on, and the magic begins. Suddenly a thin beam of light pierces the length of the cavernous space, so intensely emerald green that Krebs' large pet parrot, perched above the beam, seems to fade in its wake.

"I'm not going to be doing a typical light show at Lisner -- flick! flick! flick! all over the place," says Krebs, referring to the kind of laser extravaganzas put on at rock concerts and in planetariums. "But that doesn't mean this won't be theatrical. We'll be establishing a dramatic sequence -- in the hot spots the laser is red, and in the soft spots the laser is blue and accompanied by ground fog." These maneuvers will be carried out by the artist, who will be in the orchestra pit, and a backstage operator. The laser's light will emanate from behind the stage, guided by six mirrors located at various sites throughout the auditorium.

Working with such a powerful instrument requires certain precautions. Krebs must file his plans with the Bureau of Radiological Health. Certain seats in the house will be cordoned off. And then there's the performers' safety to consider.

"The beam is not intense enough to burn the skin, but it is certainly intense enough to burn the eyes," Krebs explains. As a result the dancers will wear protective goggles, which have their own drawbacks -- they eliminate green-blue light, at times depriving the dancers of depth perception and other visual amenities.

How are they coping?

"Some of them do have anxieties about the laser, but others have no problem," says Krebs. "The thing that really throws them is when they do their interactions with the beam, and they can't even see it."

In the far more ordinary confines of George Washington University's Building K, Withers and the eight members of her Dance Construction Company are rehearsing a movement sequence that looks every bit as challenging, and just as unorthodox, as Krebs' sculptured light.

They are dancing on stilts.

"This is the 'Jungle Grass' section of the piece," says Withers, a powerhouse of a woman with a face that could easily join those on Mount Rushmore.

She punches the tape deck, and Boilen's pulsing electronic score washes over the studio. Agile as chimps, the dancers bound from tabletops onto pairs of thick wooden stilts that reach almost to the ceiling. They "walk" in formal patterns, jump off the stilts, manipulate them like weapons, pound them rhythmically against the floor, fall flat and begin again. There's a regal quality to their movement, and a very strong sense of a community in control of its environment.

Withers dispels that notion in a flash. "You know, we've only had two sessions in which we actually rehearsed with the whole laser setup," she says. "So we're all a little nervous."