In a Double Bill of Debuts, Subtle Studies in Stillness.

Two budding choreographers shared the stage at Danspace Project at St. Mark's Church on Thursday night in a double bill that examined degrees of stillness. Tara O'Con, in ''Walk It Once,'' began her investigation in near darkness, as a dancer, using her head to burrow into the floor, revealed little more than the muscular expanse of a bare back. ''Standard Gravity, part 2b,'' by Enrico D. Wey's troupe Living Laboratory, enacted a slice of American suburbia -- or at least that's what the neat square of synthetic lawn placed in the center of the stage signified -- in which a group of dancers alternated brisk walking with stationary poses. [ABSTRACT FROM PUBLISHER]