Oberon: Ill met by moonlight, proud Titania.

"The trick is, the moon has to rise slowly," said David Glenn to an unseen technician somewhere in the nowhere above the Arena Stage. "Once the moon clears the water it can speed up."

The moon, at this point in the technical rehearsal for "A Midsummer Night's Dream," which opens today, breaks the surface of the pool built into a corner of the stage and sheds water like a sheath of silk, then ascends rather jerkily to stage heaven.

"Pick up the speed a little," calls out master carpenter James Glendinning.

The moon, that "silver bow new-bent in heaven," is nearly a character in this "Midsummer," a Shakespearean bauble that illumines the night and the madness.

Pyramus: Sweet moon, I thank you for thy sunny beams;

I thank thee moon, for shining now so bright,

For, by thy gracious, golden, glittering gleams,

I trust to taste of truest Thisby sight . . .

And for director David Chambers, it was a central image. "The moon is the lunar side, related to the female side of us. Oberon lives in the trees, the phallic side."

The moon is also actually a sphere of plastic, layered thinly with translucent paint and lit from within by a battery-powered bulb. But Chambers didn't want just a moon, he wanted a tree world for Oberon, and a pool that fairies and Titania would live in and dive into. So the set is a moonscape: latex-covered Styrofoam, a canopy of branchlike pipes hovering 12 feet above the floor, and a pool eight feet deep containing 7,000 gallons of water.

"David Chambers had this image of a moon rising out of a pool," said set designer Heidi Landesman. "The pool is Titania's sphere of influence, the tree canopy is Oberon's, and Earth is the court at Athens. We tried, in one design, grass on a flat floor with the pond, but it looked like a putting green."

"I don't know where I got that image," said Chambers. "The easy answer is that I have a house in New Hampshire that has rolling hills and a pond and trees, and then one night I was watching a very bad ballet on television, and sort of dozing, and the ballet happened to have a moon in it. That's when I realized you could have an image of a moon coming out of water."

The technical rehearsal is the final stage of preparation before the audience comes. All the equipment is suddenly there, trying to work together in smooth coordination. The actors are dressed in costumes for the first time, enchanted (usually) with their new-found transformations, and treated rather like props or performing seals during this slow exercise of technicality. Their job here is to give the cue so that others may practice dimming the lights, or raising the moon.

Originally, Chambers wanted Titania to spring out of the pool, a water nymph on a rubber band. That didn't quite work. "It's just so interesting to watch someone get out of the water," mused Chambers. "I think that's one big reason we go to swimming pools."

"We're cold," chirped the fairies from their hidden perch in the pool.

"That water is 75 degrees," said Glenn firmly.

Frozen fairies are not the only problem that has surfaced as a result of the water. "Everyone's been slipping on the floor," said Landesman. The floor is made of Styrofoam, 60 pieces that were individually sculpted, then covered with 50 gallons of latex. "It's great for tumbling," she said. "But wet, it's like ice." So it was doctored with grit, and pads were sewn onto the ballet shoes some characters wear, and the rest was up to the actors getting used to it.

"We rehearsed in the swimming pool next door and on a flat floor," said Kathleen Turner, who plays Titania and Hippolyta. She is nursing a swollen hand. "I had a sort of back dive, and I ran into the ladder.".

Turner made something of a name for herself starring in "Body Heat," a movie in which she was frequently undressed and sweating. In "Midsummer," as Titania, she wears a flesh-colored body stocking decorated with flotsam, and is often wet. The leotard dries fast; the wig and shoes don't.

In this production more than most, the actors' interpretation of their characters is influenced by the set, which has so strongly dictated the movement and the "environment" in which they live. Turner's Titania, for example, does a few tumbles, and Oberon does gymnastics on a plexiglass shield lying on the tree canopy. "We wanted an organic sense," said Landesman.

Meanwhile, Puck, who looked nude, although completely covered by a "unitard" of four-way stretch fabric, was being lowered from the ceiling as the moon rose from the pool. "We're going to delay Puck's entrance until we've got the moon visually established," instructed Chambers. "Avery Brooks, who plays Oberon , start your climb when the moon starts."

And so they tried it: moon out, Oberon up the tree, Puck lowered down. It worked.

"The play is finally a testament to the power of imagination and dreaming," said Chambers. "That they must be absorbed into our lives . . . We live in a society where cultural vision, imagination, dreaming are looked at as very suspect. The guys down the street gesturing toward the White House do not have time for the lover, the lunatic or the poet, nor does Athens in the first scene of this play. Then they have this dream and say, 'We'd better make room for these things. We need them.'