An engaging and 'thoughtfully serious' comedy from Lanford Wilson; Angels Fall Play by Lanford Wilson. Directed by Marshall W. Mason.

Lanford Wilson has gone to the New Testament for the text of the thoughtfully serious comedy with which the Circle Repertory Company has opened its 14th season. The latest Wilson work, entitled ''Angels Fall,'' has been staged by his longtime collaborator, Marshall W. Mason.

The biblical borrowing occurs late in the second act. Stirred by a challenge to his cherished career hopes for an exceptional young parishioner, the Rev. William Doherty (Barnard Hughes) turns uncharacteristically ministerial. Seizing his well-worn copy of the Scriptures, the concerned cleric exhorts his hearers with words from St. Peter's Second Epistle: ''Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness . . . ?''

''Angels Fall'' is movingly concerned about ''what manner of persons'' have been brought together in an isolated New Mexico mission chapel. The mission is within easy fallout reach of a uranium mine where an accident has occurred. The nasty predicament facing the stranded travelers is suggested by the sounds of amplified warnings broadcast periodically from low-flying helicopters. Traditional in form, the play involves a contemporary phenomenon: the incidental threats posed by a nuclear age. But it is primarily about individual responsibility, vocation, and personal fulfillment.

The travelers of the tale include an art professor-critic (Fritz Weaver) caught in a traumatic midlife crisis; his pretty wife and one-time student (Nancy Snyder); the widow (Tanya Berezin) of a noted New Mexican painter; and the youthful tennis pro (Brian Tarantina) with whom she is heading for a San Diego tournament.

The insider-outsider of the dramatis personae is Don Tabaha (Danton Stone), a surly part-Navajo who must decide between a lucrative medical research appointment and a career as a doctor serving the people of the surrounding reservation. To Fr. Doherty's impassioned insistence that Don should practice where the need is so great, the professor argues eloquently that the choice is the young man's alone.

Although Mr. Wilson's partial resolution of the central conflict seems rather too pat and predictable, the manner in which his characters reveal themselves to one another and the audience is theatrically engaging. Under Mr. Mason's sensitive guidance, the Circle Rep cast responds with winning conviction to the play's comic as well as its more touching moments, to the frequently sharp exchanges, and to the passages of Wilsonian eloquence. In the role especially written for him of the cheerfully undogmatic priest, Mr. Hughes gives the kind of endearing performance that audiences cherish and playwrights treasure.

John Lee Beatty's beautifully simple setting has been devised so that the spectators enter the auditorium via a passageway that seems part of the mission architecture. The chapel's cool interior contrasts with the glimpsed hot sunshine outside (lighting by Dennis Parichy). Jennifer von Mayrhauser designed the costumes.

''Angels Fall'' was commissioned and first presented by the New World Festival Inc., in Miami.