THE GINGHAM DOG - At the Back Alley through July 15.

It is hard to think how the Back Alley Theater could better execute its revival of Lanford Wilson's "The Gingham Dog" (1968). The performances are thoroughly professional. The set makes a virtue of the cramped quarters, inviting the audience into a Manhattan apartment where an interracial marriage has come apart.

But all the talent, and the passage of time since the rhetoric-ridden '60s, combines to emphasize how thin and unhumane was Wilson's conception. He makes carpet-tack points with sledgehammer statements, some of which are almost unspeakable.

The only worthwhile thing about the play - and it really is worthwhile - is watching the artists struggle to overcome the material. The final score is Artists 2, Playwright 2, with Back Alley's staging breaking the tie.

Mark Selinger works up an awful sweat carrying his role as a young honky architect who has sold his liberal soul to a firm of high-rise slumbuilders; he pins Wilson in the second act, largely by doing a marvelous drunk. Linda Shockley uses finesse to create depth and sympathy for the role of a black woman who left her meaningful job as a school social worker and arrived at self-loathing for being housewife to a white man while her brothers and sisters were starving in the streets. Melissa Craig tries hard but cannot save her pitifully stereotypical part as the honky's Southern belle-brain sister. Akim Nowak's role as a white-fag neighbor has no substance and no purpose, and his infectious energy is wasted. CAPTION: Picture, IN "THE GINHAM DOG" ARE, CLOCKWISE FROM THE TOP, AKIM NOWAK, MARK SELINGER, MELISSA CRAIG AND LINDA SHOCKLEY.