From Rhode Island's Trinity Playhouse, a bittersweet picture of man at war

You spend a half hour waiting for ''Billy Bishop Goes to War'' to begin. The theater has been transformed into a cavernous roadhouse complete with tables and bar, and you have to get there 30 minutes early to get a good table because, with a fistful of rave notices, ''Billy Bishop'' is packing them in at the Trinity Summer Repertory in Providence (through Aug. 28).

Not that the wait is time wasted. It takes that long to absorb the incredible detail of production-designer Eugene Lee's Canadian beer hall. Lee has worked some kind of magic with the place, creating an atmosphere in which the usual pool table, wall plaques, and gaudy bric-a-brac take on the Zeitgeist, as well as the physical placeness, of a post-World War I watering hole.

There is, however, a certain ambiguity of time to Lee's setting (witness the portrait of Franklin Roosevelt amid the memorabilia of a different age.) As if he had deliberately thrown in enough minutiae of other eras to make you wonder slightly what time frame you are traveling in.

And this is the genius of the thing. Because ''Billy Bishop'' is a story across time about a character who, although specifically fighting in World War I , might just as well be Henry Fleming proudly displaying his red badge of courage.

The Trinity Rep, one of the country's most respected regional theaters, needed a summer vehicle that would work in a cabaret set

ting; but writer/composer John Gray gives us a lot more than that. He gives us a bittersweet picture of man at war, one that includes the audience more than plays to it.

Because we are all gathered together in this thoroughly authentic place talking to our friends and watching the crowd, when this young man sits at the piano in our midst and starts playing. ''Good Bye, Dolly Gray'' ''It's A Longno comma Long Way to Tipperary.'' ''White Cliffs of Dover.'' The general hubbub dies down, and - presto! - we are in the thing itself, singing along, convivial and warm until Billy Bishop himself shows up.

Peter Gerety, who plays Bishop, is one of the most energetic and frequently effective actors that this haven of good actors in Providence has to offer. In this piece he exhibits more control and maturity than he has in a season of Trinity productions. When he comes in, the mood and the songs suddenly take on a slightly Weill-Brechtian tone.

There is a humor to ''Billy Bishop,'' but it is a humor that turns around and stings you. There are a couple of instances when this humor lapses into bad taste, by the way.

Bishop is a young man going to war. He goes because he is flunking out of school, because all of his friends are going, and because (as one of the songs puts it) ''It didn't seem like war at all.'' But it was war. And although Bishop returned in one piece to tell his tale in songs and anecdotes and some verse, he didn't return untouched.

He transferred to the Air Corps - which in those days meant planes that were ''kites with an engine attached'' - in order to avoid ''dying in the mud.'' But Billy Bishop learned more over there than how to fly. He learned how to kill, and how to like killing.

To see Peter Gerety take Billy Bishop from a callow innocent abroad to a grown man who has changed in ways he doesn't care to look at, is to see a master at work. Somehow he manages to bring you up in an imaginary airplane, and then gets you to gaze down at the patchwork earth with him.

Like some kind of Sergeant York, he holds the entire audience captive, almost single-handedly. I say almost, because Gerety gets some help from his friends. Piano player and singer Stephen Snyder keeps the music percolating. Richard Jenkins's highly energized directing has Gerety caroming off the audience like the cue ball on the pool table.

But this is Gerety's night. And with it he adds another acting medal to the long string he has earned at Trinity. It is thanks to him, and to the writing of John Gray, that ''Billy Bishop'' becomes more than a personal story.

It becomes a memory of war. Never mind which war. The point is that young men and old were dying. And it was all so needless. And ''Billy Bishop'' remembers it so well.

N.Y. Shakespeare FestivalJohn BeaufortNew York

With last season's highly regarded British imports, such as ''Plenty,'' ''Top Girls,'' and''Fen,'' the New York Shakespeare Festival touched in one way or another on concerns of women. Unfortunately, the festival has chosen to follow those earlier achievements with an offensive, two-part seminar on feminism Italian style.

Or perhaps one should call it feminism a la Franca Rame and Dario Fo, the Italian husband-and-wife writing and performing team. Their internationally successful ''Tutta Casa, Letto e Chiesa'' (literally, ''All Home, Bed, and Church'') has come to the Public Newman Theatre in an English version entitled, ''Orgasmo Adulto Escapes from the Zoo.''

Each evening's segment consists of four one-act plays - all purporting to protest the sexual subjugation of women. Their surrogates are played by Estelle Parsons in what is virtually a solo performance.

Miss Parsons is a skilled technical actress and an energetic, resourceful performer. But this marathon of grotesqueries, miseries, and left-wing cliches proves unduly monotonous and tedious for the spectator. John Masterson occasionally shares the stage with Miss Parsons as a very incidental male of the moment.

The first evening's three overlong comic sketches rely heavily on simulated sexual encounters to hammer home their ostensible message. The explicit material seems to exploit the very women it claims to champion. (The authors apparently subscribe to the notion that women somehow prove their equality and liberated state by indulging in the obscenities and crudities usually associated with male ''dirty talk.'')

The fourth and most interesting playlet in the first set is an Italian folk version of the Medea tragedy.

The second program opens with the comically rendered trials and tribulations of a working wife and mother whose long factory hours are preceded and followed by the endless domestic chores for which she receives no pay. Prison torture provides the grim theme of ''It Happens Tomorrow,'' while ''Freak Mamma'' chronicles the making of an Italian drop-out bag lady. In the final sketch, a mental patient wired to an electro-shock machine recites her harrowing life story to an unseen doctor.

If the sketches were drastically edited and reduced to about half their present number, the Italo-American collaborators might stand a better chance of making their case - whatever it is.