THE THREE SISTERS - Wednesday through Sunday evenings at 8 through July 8 at Trinity Theatre, 36th and O Streets NW.

Washington's Source Theatre Company has a well-earned reputation for skill and boldness. In its current production of "The Three Sisters," however, the company shows neither the skill to carry off Chekhov's lumbering diatribe nor the boldness to cut the play down to the size of its message.

In the time of the czars it may have been heady stuff to portray Russia's upper classes as thoughtless, aimless and spineless, but rivers of blood have washed Chekhov's 1901 chatter pale. While the lines no doubt have lost something in translation, the idiom rings so true it cannot be a bad one.

Chekhov's wife played in the original Moscow production, and one suspects he wrote in roles for other friends. At least six of the 18 parts could be dispensed with. A 3 1/2-hour play may be just the thing to while away a long Russian winter night, but over the span of time it is reasonable to expect the characters to take on some depth. Chekhov's people are clockwork cariactures with some of the gears missing. They are noisy, they are active, but they are not real.

Having elected to undertake another production of "Sisters" - the earlier run was respectfully reviewed - Source has been all too faithful to the work. If the players cannot bring themselves to discard the surplus verbiage, they might at least deal with it more speedily. Lines that should flit past like cocktail conversations are laid down one by one, like bricks.Even the brief moments of comedy relief seem studied.

The fine sets, professional staging and conscientious efforts of the cast are admirable but in the end not engaging. Source is a fountainhead of serious theater in Washington; in this case, too deadly serious. CAPTION: Picture, THERESA ACEVES, LEFT, MEGAN MORGAN AND MICHAELEEN O'NEIL, KNEELING, IN THE SOURCE THEATER'S PRODUCTION OF CHEKHOV'S "THE THREE SISTERS."