Two plays that seek the pulse of national problems; The Harvesting Play by John Bishop. Directed by Mr. Bishop

The grimy environs of a small Midwestern city provide the setting for the grim events of John Bishop's ''The Harvesting,'' which is being given its world premiere by the Circle Repertory Company on Sheridan Square. Mr. Bishop has written a crime drama with sociohistorical trimmings as he sets detective John Torski (Jimmie Ray Weeks) to work solving the murder that has just been committed as the lights go up.Detective Torski's investigation takes him back in time to a fatal case of child abuse which occurred some 20 years earlier - a case he failed to solve even though he suspected the truth about the crime. Torski's determination somehow to atone for that earlier failure intensifies his compulsion to arrest the man he believes guilty of both crimes. His chosen suspect is Bim Miller (Edward Seamon), a ruthless wheeler-dealer whose manipulations the detective holds responsible for the physical and spiritual decline of Mansfield, Ohio, where the play is set.As Torski and his fellow detectives (Paul Butler and James McDaniel) pursue the scant leads in the case, Mr. Bishop reveals the background of troubled relationships in the Miller family. Besides the menacing Bim himself, there are his pathetically disoriented daughter, Joyce (Jane Fleiss), and his returning son, Tommy (Timothy Carhart), who was sent away from home after the original tragedy and has grown up under another name.Crime solving, however, is only one of the things on the author's mind as clues are followed and interrogations conducted. Like its metaphorical title, ''The Harvesting'' concerns Mr. Bishop's bleak view of certain aspects of Americana and their sociological implications. The action occurs in the course of the four days leading up to the 1976 American bicentennial. The final confrontation occurs amid the offstage sounds of celebratory fireworks.In his effort to touch as many bases as possible, Mr. Bishop risks a certain amount of arbitrary contrivance. The play abounds in references to relevant subjects - from the Vietnam war to the sometimes precarious status of upwardly mobile blacks in white America, from the vanished steel mills of an earlier industrial era to urban decay. Says Torski: ''When they tore the courthouse down, they tore the heart out of this city.''Yet ''The Harvesting'' preserves its franchise as a taut example of theatrical detective fiction, with a requisite number of plot twists, surprises, and climaxes. Meanwhile, the overheard radio conversations of police officers as they cruise their precincts introduce some comic ribaldry and add to the nitty-gritty atmosphere of cops at work.As director, Mr. Bishop has staged a thoroughly believable performance, paced by the ever reliable Mr. Weeks , with notably strong contributions by Mr. Carhart, Miss Fleiss, and Mr. Seamon. The Circle Rep production attempts an environmental effect by having designer Loren Sherman create a four-wall, black-and-white cityscape panorama. The visual results are scarcely impressive enough to justify the effort. What counts is the action that unfolds on the all-purpose square stage of drab linoleum tiling, with minimal props and furniture to suggest changing locales. ''The Harvesting'' was lighted by Mal Sturchio and costumed by Ann Emonts. The Flight of the Earls. Play by Christopher Humble. Directed by Allen R. Belknap.

The human toll of Northern Ireland's civil strife and uncivil violence is brought home to a County Tyrone farmhouse in ''The Flight of the Earls,'' at the Westside Arts Theater (Downstairs). Playwright Christopher Humble accentuates the gender gap that separates the womenfolk of the Earl household from the three brothers who have committed their lives - and the lives of unsuspecting others - to IRA terrorism.The time of the action is 1971. Widow Kate Earl has long since condemned the cause that took her husband's life. In their turn, her three grown sons (Guy Paul, Timothy Landfield, and Kenneth Meseroll) have been busily constructing a secret bomb factory underneath the family-owned garage and plotting to assassinate the prime minister on his forthcoming visit to the area.The ruthlessness of the terrorists emerges in other ways. The hard-earned money Brigitte Earl (Christine Estabrook) has been giving husband Michael (Mr. Landfield) to procure brother Keith's release from prison has actually been going to finance the terrorist cause. It turns out that Keith has been free and in hiding for months. Furthermore, Ian and Michael attempt to engineer the bomb death of Brigitte's retarded younger brother when they fear that, as an unsuspecting courier, he has become a security risk.While Mr. Humble allows the Earl brothers to plead the Irish Catholic cause against British and Protestant rule, ''The Flight of the Earls'' eloquently disavows what widow Earl labels the poison of violence. Otherwise, the author settles for melodramatic plotting rather than an in-depth examination of a tragic impasse.On the credit side, Mr. Humble makes his local debut with a compact, earnest, well-observed work about a contemporary national tragedy. ''The Flight of the Earls'' merits the commitment with which it has been mounted under Allen R. Belknap's direction.The acting of the three brothers accentuates three faces of fanaticism. Miss Estabrook gives a touching portrayal of the wife who dreams of escaping with Michael to America and whose dreams are betrayed. There are strong performances by Miss Teitel as the embittered matriarch who has taken to tippling, by Reed Birney as Brigitte's brother, and by Peggy Schoditsch as her sister, who heads a women's peace movement.Designer Lawrence Miller has provided a pleasantly low-ceilinged living room for the action, with costumes by Susan A. Cox and lighting by Richard Winkler.