A lavish, exuberant season at the Oregon Shakespearean Festival; 'Man and Superman'

The festival has given surprisingly short shrift to George Bernard Shaw over the years, but makes amends this season by giving ''Man and Superman'' the full treatment. To perform Shaw's magnum opus in its entirety requires some five hours. Most producers solve the problem by omitting the third act, which consists primarily of a long, abstract dream sequence, known as ''Don Juan in Hell,'' which Shaw wrote to be severable from the rest. All too often this philosophical balance to the main comedy is simply cast aside, but the festival to its credit has produced the piece separately in its ''studio theater,'' the Black Swan, using the same cast.

James Moll's staging of the larger comedy is a delight in and of itself: Performances are masterfully arch and sophisticated, sets by William Bloodgood are imposing, and Martha Burke's costumes are sumptuous. Moll and his actors succeed at their basic charge; they create thoroughly satisfying theater out of language and idea.

Yet if at all possible, the playgoer would be well advised to see ''Don Juan in Hell'' on the same visit. Not only does the explicit philosophical argument give the comedy in ''Man and Superman'' greater resonance, but the two productions balance each other theatrically as well.

In the main-stage comedy, for instance, Joe Vincent gives a forceful performance as Jack Tanner, Shaw's philosopher-hero, yet his style (as opposed to his character) seems a bit on the bombastic side at times. But in the role of Don Juan, Tanner's abstract, Vincent's approach is beautifully appropriate. His performance seems the stronger when Tanner is related to his archetype. Likewise , taken by itself, Joan Stuart-Morris's portrayal of Ann Whitefield, the female side of Shaw's dialectic, as a self-sure vamp is a bit excessive. But she is so much the embodiment of primal womanliness in ''Don Juan'' that her Dona Ana lends weight to her Ann.

Festival audiences will perhaps be challenged most sternly by Dennis Bigelow's production of ''The Entertainer,'' John Osborne's bleak survey of hollow patriotism and social degeneration in the Britain of the Suez crisis era. Bigelow's direction is rather physically repetitive, but he does create the sense of claustrophobia and hopelessness Osborne's work demands.

The production features an irresistible performance by the redoubtable Denis Arndt as Archie Rice, the third-rate music hall performer of the title. In a perverse way, Arndt is a bit too good; he is so thoroughly entertaining, and we have such a good time with him, that it is hard to take his nastiness and emptiness seriously.

Fortunately, Arndt is surrounded by several other strong performers who preserve a balance in tone: William McKereghan as Archie's nostalgic father, Zoaunne LeRoy as his oppressed and alcoholic spouse, and Helen Machin-Smith, doing yeoman work in the exceedingly difficult (because underwritten) part of Jean, the troubled daughter being sucked into the vortex of her father's lack of values.