An attractively mounted double bill of short works by Irish dramatists has been playing at the downstairs Susan Bloch Theatre on West 26th Street. The program comprises Brian Friel's tenderly touching ''Winners'' and George Bernard Shaw's 1904 one-act trifle, ''How He Lied to Her Husband.'' The result is a superior entertainment made up of contrasting moods, periods, and social strata.
''Winners'' takes a caring look at the frailty of human hopes and expectations. Teen-agers Mag (Kate Burton) and Joe (Michael Butler) are about to take their final school tests, almost immediately after which they will get married because Mag is pregnant with Joe's child. Yet they are still little more than children themselves. They have climbed to a hill overlooking Ballymore for a last day of intensive study before the examinations. The year is 1966.
Mr. Friel interrupts their study to acquaint us with the lives of these young people - their differing backgrounds, family milieus, and expectations. Although capable of clowning, Joe is basically studious, hoping to further his education and become a teacher. Mag is romantic, whimsical, witty, and mercurial. She likes to think that ''real happiness was never discovered until we discovered it.'' She prefaces one of her giddy verbal flights by remarking, ''Before I go silent for the rest of the day. . . .''
Of course, this delectable chatterbox doesn't go silent. The silence comes in an aftermath to the day's outing, a tragic event presaged in the intermittent narration by two commentators.
The skill with which Mr. Friel presents the shifting moods - and particularly the rapture - of the final day in the lives of two young people is matched by the appealing quality of the performance staged by Nye Heron. Miss Burton's Mag is ingenuously antic and playful, a naive adolescent capable nevertheless of sudden, acute concern over the prospects of motherhood. In Mr. Butler's portrayal, the control with which Joe masks his underlying apprehension cracks only in a momentary flare-up. Roundabout Theatre Company has mounted a sensitive revival of an appealing work. Shaw on the lawn
In their invaluable ''Theatrical Companion to Shaw,'' Raymond Mander and Joe Mitchenson recall that ''How He Lied to Her Husband'' was Shaw's practical joke on the actor Arnold Daly. Daly had requested a play ''about Cromwell.'' Shaw's response was to place the action of his one-act comedy in London's Cromwell Road.
The Roundabout Company has taken things a step further. The grassy mound designed by Roger Mooney for ''Winners'' serves (with slight rearrangements) as a greensward for ''How He Lied to Her Husband.'' So the scene of the Shavian curtain-raiser has been shifted from drawing room to lawn and from London to Ballymore House in Northern Ireland.
Shaw's miniplot concerns a husband's discovery that his wife, Aurora, has been the subject of love poems by a young admirer. The amusing playlet is acted with stylish airs and graces by Mr. Butler (He), Miss Ruskin (She), and Mr. McInerney (Her Husband).