THE director and actors of the new Loeb production of Chekhov's The Three Sisters go about their work like musicians approaching an old score with reverence but concern. They chip away at crusted traditions to reveal a musical substratum running under the characters, explaining the emptiness of their lives. This underlying music--on which director Peter Sellars has focused both literally and thematically--softens the desperate boredom of Chekhov's characters, but it also carries their despair home with sentimental poignance.

Sellars could not have entrusted the difficult task of unearthing this music to a more talented cast. Every role, large or small, gets its due; Sellars relentlessly exploits the Loeb's strength as a theater of monumental scope; lighting, sets and music all add their evocative sorcery.

Director Sellars and set designer Gary Lovesky have created a visually breathtaking production--they dragged 30 live birch trees from the Harvard Forest and ringed them around the spare, vast, white-draped stage. Huge birches and the bare exposed Loeb stage dwarf the actors and frame Sellar's epic interpretation. The Loeb production emphasizes the tableaux over the characters, but it does so with a brilliance in staging that brings out Chekhov's geometry and starkly, pictorially dramatizes the characters' relationship to each other. The operatic staging also serves to divorce the characters from the world outside the Prozorov mansion, emphasizing their isolation. Their grand gestures and melodramatic speeches seem absurd and meaningless, as observed from a distant height.

ALTHOUGH the set and staging focus on the sweeping, impersonal forces that deprive the characters of happiness, Sellars does not neglect the dense psychology of the play. In a flash of inspiration, Sellars enlisted Roy Kogan '80, to play Chopin preludes and nocturnes throughout Three Sisters. Kogan's forceful and sensitive musical interpretation adds new emotional dimension. Kogan and Sellars have obviously collaborated to fuse the music with the staging to intensify or soothe the action. In the opening of Act III, as a huge fire rages throught the town and the family's restrained tensions burst into open conflict, Kogan pounds a demonic prelude, forcing the actors to scream out their anger and pain.

More subtly, however, Kogan's tour de force helps to uncover the structure of Chekhov's play, composed in part of a series of ceaseless competing refrains of leitmotifs. Irina sighs her frustrated desire to go to Moscow, Vershinin "philosophizes" and bewails his marital misfortunes, and Natasha inanely shrieks her mother love--all accompanied by recurring Chopin preludes.

Hans Tobeason's lighting helps to transform the entr'actes and set changes into complements of the action. In these transitions, the lights shade from lavender to deep blue to gray, mirroring the emotional metamorphoses from act to act.

The lighting and the music immeasurably enhance the performance's emotional atmosphere, but the production escapes detachment and coldness chiefly because of uniformly excellent acting. Every actor crafts and sustains a character; even the bit parts are people with distinct--if annoying--personalities. Heitzi Epstein (Olga), Jenny Cornuelle (Masha) and Anne Clark (Irina) turn in carefully sustained and sensitive performances as the three sisters whose emotional foibles and frustrations are the play's heart. Clark as the youngest sister deftly moves from lighthearted young girl to pensive despairing woman. In one scene she darts across the stage, childishly reveling in the attention she receives; in the next, she stonily recalls her former happiness and despairs of finding fulfillment in work or love. Clark uses a completely different tone, inflection, gestures and stage movement to differentiate the younger and older Irina.

Cornuelle's spare acting aptly characterizes Masha, the bored middle sister tied to a pompous posturing schoolmaster husband. She rigidly controls her movements, gestures and voice, yet manages to convey Masha's emotional conflict, especially her moving confession of love for Vershinin.

Epstein portrays the maternal spinster sister Olga with convincing intensity, though she occasionally relies too much on grimaces to convey Olga's pain.

FINE performances in the rest of the cast match the skill in the title roles. Paul Redford is brilliant as Andrey Prozorov, the brother and owner of the estate, whose dream of becoming a university professor is frustrated by a tragic marriage to the bourgeois Natasha (Grace Shohet). Redford skillfully makes the transition from idealistic brother to alienated bitter council member. He epitomizes Andrey's awkwardness in his shuffling, hesitant walk and bursts of speech. And Shohet is deliciously annoying as the pushy, vulgar Natasha, who does nothing but drool--loudly--about her children.

The suitors who flock about the sisters are also well-played. John Bellucci masterfully plays Vershinin, the philosophizing soldier with whom Masha falls in love. Bellucci works his rich and versatile voice like a musical instrument, retaining extraordinary control of volume, diction and timing in long, technically taxing monologues. He meticulously defines his character by pacing constantly around the stage in repeated circles that parallel his sermons.

Laboring under the burden of a broken toe, Bellucci nevertheless is eloquent and convincing, especially in the beautifully acted love scenes with Masha. Chris Clemenson takes the awkward character of Tusenbach and fills it out with sympathy and skill. Tusenbach's paeans to labor can easily turn into sermonizing and his devotion to Irina into sickening self-abasement, but Clemenson doesn't self-dramatize the role. He transcends the limiting qualities of the part as Chekhov wrote it to create to subtle portrait of human suffering, weltschmerz and all.

Sellars seems to have let his actors develop their own interpretations, chosing to focus on creating a series of stage pictures that reinforce their interpretations. His monumental style, however, is least effective at the very beginning, where a touch more continuity and less mannerism might help the actors introduce themselves and the play's refrains. As it is, the opening portrays the prosaic daily life of the Prozorov household and friends with jerkiness. Perhaps Chekhov intended a sense of alienation from the start, but that shouldn't make the actors themselves look uncomfortable on stage, as they do for the first 15 minutes.

The Three Sisters is long--it runs about three hours--and Sellars' habit of freezing the scene at key moments doesn't speed it up any. But the Chopin behind it all transports the audience into the contemplative melancholy of the play itself--leaving audience, actors and playwright running at the same speed. The tempo lags only in the final act. With bare stage, static blocking and house lights turned up, the staging is faithful to Chekhov's sense of desolation, but also somewhat trying to an audience at the end of a three-hour haul.

But these flaws in Sellars' production stem more from inevitabilities in Chekhov's play than from major failures of direction. The Loeb crew finds the pulses and rhythms of The Three Sisters and lets them dictate the approach. The result is a show that moves, inspires, and sometimes sings in a lonely, tortured voice.