Moral malaise in middle-class America.

Serenading Louie. Play by Lanford Wilson. Directed by John Tillinger.

The resourceful Second Stage has opened its fifth season with an illuminating production of Lanford Wilson's ''Serenading Louie.'' Premiered in 1970 and presented here in 1976, the study of middle-class Americans in midlife crisis has been revised for the present occasion. It would be hard to imagine a performance of greater sensitivity and perception than the one being given under John Tillinger's direction at the Public Theater/Other Stage, where Second Stage is a guest company.

At first sight, the glossy, comfortably furnished setting for the conversations looks like the kind of living room many a spectator would happily move right into. But it soon becomes evident that malaise hangs over the premises like a pall of smoke from an autumn leaf bonfire. (The action takes place in the week beginning with Halloween.)

Carl and Mary, Alex and Gabrielle, the two couples of the drama, are coming uncertainly to grips with problems of marriage and career undreamed of a decade before in their undergraduate days. Like the poor little lambs of which they sing, these privileged young marrieds have lost their way. Even the picture-windowed, glossy chic of their suburban Chicago domiciles comes to seem like a symbol of entrapment rather than freedom. (A single setting creates an identical mise en scene for both households.)

In a series of brilliantly written conversations, Mr. Wilson probes the disappointments and frustrations of his four golden graduates. Although the dialogue can be comic, the author's sense of concern is always evident. Carl (Jimmie Ray Weeks), a Big Ten football star who has matriculated into corporate careerism, rightly suspects that wife, Mary (Lindsay Crouse), is being unfaithful to him. Alex (Peter Weller), a successful lawyer with vague social concerns and the prospect of a Washington political post, has been meeting clandestinely with a young university student. It is part of his escape from an unsatisfactory marriage to the beautiful but unsettled Gabrielle (Diane Wiest).

The men's situations are more fully and clearly articulated than those of their wives. Responding to the Wilson portraiture, Mr. Weeks presents Carl as a one-time naive who cannot face the most shattering blow to his romantic illusions. In a performance of intense concentration and subtle shadings, Mr. Weller reveals how Alex's sharp intelligence is no help in coping with emotional disarray. Although given less to work with than their male colleagues, Miss Wiest and Miss Crouse create the requisitely distinctive portraits of two women: the one neurotically near the breaking point, the other almost a detached observer of the marital havoc she has caused. Taken as a whole, the performance at the Public is a classy piece of ensemble work.

In a good many of his plays, Mr. Wilson ameliorates his more melancholy observations with an affirmative note - sometimes a strong one. There is no such mitigation in ''Serenading Louie.'' This drama of forlorn and even violently tragic consequences offers no consolation. The moral of the work is in what it observes of the moral vacuity surrounding many an apparent success story. Even in its revised state, this is a somewhat uneven work. But there is no denying its integrity and powerful effect. The production was designed by Loren Sherman (setting), Richard Nelson (lighting), and Clifford Capone (costumes).