For its current "Family as Subject Matter in Contemporary Art" exhibition, the Washington Project for the Arts came up with the mad idea of commissioning a family to create a performance piece about a family. The wacky, wonderful and inspired result, "Do You Know What Your Children Are Tonight?," which opened Thursday night, has a ring of truth underneath its brazen surfaces.

The piece is set forth by its authors, four members of the Allen family of Fresno, Calif., all of them writers, visual artists, musicians and performers. Terry and Jo Harvey, parents in real life and the mom and pop on stage, are joined by their teen-age sons Bukka, a gifted songwriter and pianist, and Bale, an artist, writer, actor and crackerjack drummer.

What the four have come up with is a brash, erratic collage of songs, sounds, images, monologues and characterizations, based on their own familial experiences but exactly to what extent it's hard to know. The whole shape and tone of the thing is indelibly American, in its lingo, its bawdy irreverence, its cheerful sprawl and clutter, its rough and tumble pace, its flair for yarn-spinning, and in the way it turns the sentimental cliche's of American family life topsy turvy.

It's as if the Norman Rockwell vision of the American family were filtered through Hiroshima, Vietnam, the moon landings and angel dust, and then translated into lyrics for a folk-country-rock music festival. The piece is serious, however, only in its overtones -- the prevailing mode is comedy even if some of the humor is grim. The family according to Allen falls somewhere between Sam Shepard and Jean Shepherd.

The opening scenes come at you through a haze of ambient noise -- telephone rings, loud knocks, scraps of TV news bulletins. Slides of family photos, doodles and drawings, cartoons and other atmospheric items are projected on a wall, near which is Bale's drum set. In a corner is an armchair from which mom and dad take turns delivering their wisdom; in another is a piano and microphone for the songs. There's also a tall red ladder and some other props, but downstage, on a table littered with cereal boxes, is a rabbit-eared television, obviously the hub and altar of family life.

Bukka sings songs about skulls, scabs and werewolves (he and his brother are members of Fresno's Teenage Nightmare Band). One of the boys plays with an electric toy car and then stabs it repeatedly with a switchblade knife. Mom nags them -- "do your homework, fill the goldfish bowl like I told you" -- and worries aloud to the audience about whether they're into drugs, VD, abortions, car wrecks or muggings. "Worst of all," she laments, "they could be queer -- you'd be the last to know." Later on she grows defiant, tells us she's an actress not a housewife, reminds us that she was fifth runner-up in the Miss Texas contest, and if she ever found Mr. Right, "I'd go to Hollywood and leave all this behind just like that." There are musings about divorce, infidelity and making love in automobiles.

Perhaps the heart of it all is contained in a line from one of dad's songs: "Most certainly seems some disease of the dreams been goin' around." And yet, and yet -- for all the malaise, real and imagined, portrayed in the piece, there's this terrific undercurrent of commiseration, compassion and affection. At the end, the four artists join in a "family song" by Terry, and the huggings and smiles aren't just a fact of the Allen clan's existence, but somehow as well, a symbol of the very special warmth American families are capable of generating. It's the combination of razzing and warmth that gives "Do You Know What Your Children Are Tonight?" an added fillip of appeal all through.

The performance repeats a final time tonight.