In The Sweet, Funny By and By OIL CITY SYMPHONY

In a pennant-festooned high school gymnasium in the imaginary Midwestern town of Oil City, four musicians who grandly call themselves the Oil City Symphony have come together for a reunion concert. There is Mark the pianist and accordionist, a geek with glasses in a white dinner jacket and purple slacks who is also the minister of music at his church; Debbie the drummer, an ex- prom queen in a strapless gown who exchanges one pink pump for a running shoe, the better to thump her bass drum; Mary the violinist, of stern Scandinavian stock, uptight, humorless and "best remembered locally for her performance as Anita in West Side Story"; and Mike the gentle, wistful synthesizer player who found himself during the 1967 Summer of Love and once played with an acid- rock band called Thursday's Grief. They are terribly earnest, terribly sincere and just plain terrible. If it really is hip to be square, the Oil City Symphony is further along the cutting edge than the Talking Heads.

Musical humor is no joke to perform, but it can be very funny, and Oil City Symphony, now playing at the downtown branch of Manhattan's Circle in the Square Theater, is very funny indeed. Whether grimly trying to keep up with the quickening abandon of a mock Hungarian czardas, or haplessly segueing from Verdi's "Anvil Chorus" to Iron Butterfly's In-a-Gadda-Da-Vida, or just getting down and funky with a little tune of their own called Beaver Ball at the Bug Club, the Oil City Symphony lets the good times roll, and in the process skewers every high school music program in the country.

But fondly. The accomplished performers who wrote the show and some of the musical selections -- Mark Hardwick and Debra Monk (who collaborated previously on the 1981 off-Broadway hit Pump Boys and Dinettes), Mary Murfitt and Mike Craver -- are all Middle Americans by upbringing, not New York City wise guys. They've been there. When Debbie sings an ode to shopping malls and interstates called Ohio Afternoon ("Ohio fun . . . diesels dragging out on Highway 1"), she gets all misty. When Mark and Mike have at a couple of Zez Confrey ivory ticklers like Dizzy Fingers and Coaxing the Piano, their doofus grins proclaim the triumph of diligent drudgery over inspiration. No wonder Miss Reeves, their music teacher, is beaming.

In this mock recital, everything is played for real. Seated on folding chairs on the gym floor, the spectators are treated as if they had been classmates in Oil City, and each night a different woman in the audience is -- surprise! -- showered with affection as "Miss Reeves." While it is easy to make fun of ineptitude, it's quite another thing to make it sweet and touching. When Debbie and Mary can get a seen-it-all, done-it-all Greenwich Village audience on its feet, unabashedly doing the hokey-pokey and, later, singing a tender, hushed chorus of Joseph P. Webster's 1868 pop-religious hit Sweet By and By, they deserve to be proud as punch. After the performance, in fact, they even serve punch in the lobby; right to the end, the joke is on us. "One thing that we've proved tonight, surely," says Mark, near the end of the show, "is that music never goes out of style." Not when it's played like this.