Winter Theater's impressive 'Trespassing' treads grim territory; Trespassing. Theater piece by the Winter Project. Directed by Joseph Chaikin.

There is no other theater group like the Winter Project. Once a year, from wherever they have wandered, its members gather in New York to create a new production, led by director Joseph Chaikin. After a brief run, they disband again until the next season.

Lately there has been worry about the company's ability to maintain this eccentric schedule, given the hard realities of time and money in the rarified world of experimental theater. But for the time being the Winter Project is alive and well, performing a new piece called ''Trespassing'' through March 21 at La Mama.

The main character of ''Trespassing'' is a dying woman, played by Gloria Foster. Reclining on a wooden platform at the center of the stage, she laments, protests, and tries to understand her condition. Meanwhile she is visited, comforted, puzzled over, and ignored by a procession of minor characters, who range from compassionate to well-meaning to simply ridiculous.

It's often a grim show, swinging between the anguish of a ''Cries and Whispers'' and the pitch-black humor of a ''Whose Life Is It, Anyway?'' with moments of stunning insight that surpass either of those previous efforts. Calling on the versatility that has served them so well in the past, the Winter Project members do an impressive job of playing a long list of personalities, from cold professionals to friends and relatives who are variously bumbling or irrelevant or both.

The action is slanted more toward storytelling than was last year's Winter Project production -- the excellent ''Tourists and Refugees No. 2'' -- but it is still far more impressionistic than realistic. The set by Jun Maeda, lighting by Jane Hubbard, and onstage sculpture by Mary Frank are consistently eloquent. The action flows seamlessly under Chaikin's guidance, punctuated with moments of sheer visual brilliance.

Yet through it all runs a feeling that this particular subject matter is too broad and too deep to be nailed down, even by this talented and dedicated troupe. As the title indicates, ''Trespassing'' encroaches on strange and forbidding territory. The exploration is impressive, but neither as thorough nor as evocative as one might wish.