The comedy and the drama of families facing change Tomorrow's Monday Play by Paul Osborn. Directed by Kent Paul.

The Circle Repertory Company has opened its 1985-86 season by alternating two comedy dramas from earlier periods -- the first from the 1930s, the second from the 1940s. Both works are portraits of families facing change. ``Tomorrow's Monday,'' by Paul Osborn, introduced the tandem offerings. Concerned with an unexpected weekend in the lives of a Midwestern family, the play was written in the 1930s, opened in Brattleboro, Vt., in 1936, and is being performed in New York for the first time. ``Tomorrow's Monday'' belongs to the period of Mr. Osborn's two early hits, ``The Vinegar Tree'' and ``On Borrowed Time,'' and the belatedly successful ``Morning's at Seven.''

``Tomorrow's Monday'' takes an affectionate look at some recognizable human beings of a bygone generation. The play deals with the return home, after a seven-year absence, of Richard Allen (Richard Backus), who has carved out a New York business career and married a wealthy sophisticate. The couple's sudden visit has been prompted by an urgent wire reporting the serious illness of Richard's mother, an elderly widow, Mrs. Allen (Helen Stenborg). The report proves to have been exaggerated by daughter Est her (Trish Hawkins). Serene and cheerful, Mrs. Allen emerges from the sickroom to resume her role as mother and hostess. What has not been foreseen by anyone but Mr. Osborn is the havoc created by Richard's wife, Lora (Diane Venora).

The play's emerging crisis centers on Lora's effect on young John Allen (Robert Macnaughton), a college sophomore dissatisfied and uncertain about his future. John responds enthusiastically to his liberated, slightly Bohemian sister-in-law, particularly when she suggests that he return with her and Richard for a New York visit. Mrs. Allen greets the invitation philosophically, while overpossessive Esther schemes desperately to keep her younger brother tied to his Midwestern moorings.

In characteristically humane fashion, Mr. Osborn uses the effects of the homecoming to create a study of attitudes -- mostly humorous but sometimes painful. If ``Tomorrow's Monday'' seems not fully focused, that is perhaps because no single protagonist emerges. The playbelongs equally to its principal characters. The production staged by Kent Paul can appear restless, but the characterizations are vivid. The ensemble performance owes its effectiveness equally to Miss Venora's coolly captivating Lo ra, Mr. Macnaughton's naive John, Miss Hawkins's meddlesome Esther, Miss Stenborg's comfortingly practical Mrs. Allen, Mr. Backus's troubled Richard, and Amy Epstein's touchingly honorable Mary Davis (John's girl).

John Lee Beatty designed the all-purpose parlor setting for the two-play repertory, with lighting by Dennis Parichy. The costumes for ``Tomorrow's Monday'' are by Jennifer von Mayrhauser. Talley & Son Play by Lanford Wilson. Directed by Marshall W. Mason.

Retitled ``Talley & Son'' and somewhat revised since its 1981 premi`ere, Lanford Wilson's third play in his Talley family cycle completes the current Sheridan Square repertory. It remains a conventional, heavily plotted comedy drama about the workings of greed, manipulation, and cunning within a household of odious Missourians. The action takes place on Independence Day, 1944, paralleling the events of ``Talley's Folly,'' the romantic comedy in which Matt Friedman woos and wins Sally Talley.

The new title replaces ``A Tale Told,'' a quotation adapted from Psalms 90: ``Thou hast set our iniquities before thee, Our secret sins in the light of thy countenance. For all our days are passed away in thy wrath: we spend our years as a tale that is told.''

The iniquities and secret sins of the Talley menfolk emerge in the course of sometimes comic altercations as the family welcomes home elder son Buddy (Lindsey Richardson) from the war in Europe and awaits the arrival of younger son Timmy (Mr. Macnaughton) from the war in the Pacific. Timmy, however, has been killed on Saipan and serves the play as a ghostly commentator.

``Talley & Son'' focuses on the unequal encounter between detestable old man Talley (Edward Seamon) and his weakling son Eldon (Farley Granger) over the disposal of the family's war-prospering textile factory. The ancient patriarch has a nasty way of springing back from his lapses into senility and deafness to outmaneuver everyone in sight. There is dirty work aplenty in the Missouri farmhouse as the author tallies the assortment of iniquities and secret sins.

The play appears to have retained its original thrust in Mr. Wilson's new version. The spectral Timmy figures more prominently, serving as a gentle counterpoint to the acerbities of the mortally ill Lottie Talley (Joyce Reehling Christopher), who regards her bigoted and predatory kinfolk with well-deserved contempt.

The current productions mark Marshall W. Mason's welcome return to artistic directorship of the Circle Rep after a two-year sabbatical. The fine performance of ``Talley & Son'' guided by Mr. Mason includes Miss Stenborg as Eldon's gradually undeceived wife, Mr. Backus as a Talley partner in business and avarice, and Laura Hughes as Buddy's pathetically tiresome wife, as well as Lisa Emery, Julie Bargeron, and Steve Decker as a trio of underprivileged locals who make the mistake of trying to outsmart ol d Talley.

Laura Crow designed the costumes for ``Talley & Son,'' which is scheduled to run in repertory with ``Tomorrow's Monday'' through Nov. 24.