For the CSC's austere and restless 'King Lear,' the accent is on words; King Lear. Tragedy by Shakespeare. Starring Robert Stattel. Directed by Christopher Martin for CSC Repertory.

Here is a theater company that thrives on challenge.

Its past season included the complete ''Oedipus'' plays of Sophocles. This year's repertoire already includes the uncut ''Peer Gynt'' of Ibsen--all five hours of it--and ''The Cherry Orchard'' by Chekhov.

Now, just when you'd think it was time for a breather, the troupe has plunged into Shakespeare. And not just any Shakespeare, but the long and arduous ''King Lear'' - presented in the usual CSC style, with the accent on words instead of frippery.

As always at the troupe's Greenwich Village theater, the stage is largely bare. Props are carted in when necessary: the stocks for Kent's punishment or the map on which Lear outlines his fateful plan for dividing his kingdom. For the rest, language must suffice, punctuated by an austere lighting design (a few flashes to indicate the storm) and a speck of electronic music in place of trumpets. The costumes are similarly forthright, having a vaguely contemporary look, leathery at times.

Such a bare-bones approach sometimes makes things a little dull at CSC, visually speaking, but for ''Lear'' it seems grimly appropriate. In the conception of Christopher Martin, director and designer of the show, ''Lear'' is all about the ''empty space'' that ensues when an old way of life cannot hold and a new order has not yet taken its place. Thus the wide-open stage implies a restless and unfulfilled state of mind, as well as a society in tumultuous transition.

The title role is played by CSC's current leading man, Robert Stattel. A capable and experienced actor, he has the voice for Lear - a resonant voice that reaches thunderous heights in moments of rage and despair. He rests on ordinary gestures and easy ironies at times. Yet he carries the role with authority and rises to excellence in his most passionate scenes. It is a strong showing in a part of legendary difficulty.

The sturdy CSC company backs him up well. Brian Lawson is a likable Gloucester, though he is inadequate for the difficult scene in which his character is blinded. Patrick Egan is a roguish Edmund, while Tom Spackman as Edgar moves convincingly from nondescript to assertive. Patricia O'Donnell is an exquisite Cordelia; Karen Sunde is a shifty Goneril; and Carol Shultz is an effective contrast to both of them as Regan. The gifted character actor Tom Spiller is a doughty Kent, and Noble Shropshire - who also composed the brief music in the production--is a Fool of impressive peculiarity.

CSC, also known as the Classic Stage Company, will continue its virtually uncut ''Lear'' in repertory with ''The Cherry Orchard'' and ''Peer Gynt'' until Easter, when Strindberg's dark and bizarre ''Ghost Sonata'' (replacing the originally announced ''Maskerade'' of Lermontov) will round out the season.