The Allens of Fresno, Calif., are a ready-made "Family as Subject Matter in Contemporary Art." Tomorrow night they bring their play to the Washington Project for the Arts' mixed-media exhibition of that name.

Writer and performer Jo Harvey Allen, her husband, artist and musician Terry Allen, and their two teen-age sons Bukka ("named for blues singer Bukka White") and Bale (short for "Beowulf") are here to perform their hour-long play "Do You Know What Your Children Are Tonight?," which the WPA commissioned one year ago.

The play, Jo Allen says, is "about an American family" and "runs the gamut . . . It's a mixture of comedy, drama, poetry and music."

Bukka and Bale wrote and will perform much of the music. Bukka is a "rock 'n' roller," Jo Harvey Allen says. Terry Allen is on Texas roads much of the time with his country-rock Panhandle Mystery Band, and earlier this year his installation piece "The Embrace" appeared in the Hirshhorn's "Content . . ." show.

In "The Embrace," a room was encircled by bleachers. In the middle a small boxing ring with a television set played a videotape of a man and a woman acting out different aspects of their relationship. Jo Harvey Allen played the woman, and WPA director Jock Reynolds played the man.

Terry and Jo were "high school sweethearts" in Texas and married 18 years ago. They live in Fresno because "it's out of the way" and provides a "good family environment," says Jo, who is on the road herself much of the time with one-woman performance pieces.

"Do you Know What Your Children Are Tonight?" opens at 8 p.m. tomorrow at the WPA (400 Seventh St. NW; 347-4813) and runs through June 29. Admission is $5-7.