IN a former life, the rickety wood-frame Victorian on San Francisco's Potrero Hill - a racially mixed working-class neighborhood with a gradual yuppie influx - was a Methodist Church. Today it is the studio of the Pickle Family Circus.
On most days, bars of circus-style bebop and swing float out to the sidewalk. Some nights, neighbors see Indian clubs and trapeze riggings sail past upper windows.
But on Saturdays, sights and sounds shift. At regular intervals, small groups of children in leotards, sweats, and droopy leg-warmers burst in and out of the creaky double doors.
On this particular Saturday, the only music is the shrieks of giggly moppets as Judy Finelli, the Pickle Family's ''juggler extraordinaire,'' demonstrates the whirling diabolo, a yo-yo-like top that whips, dives, and whines along a six-foot string.
''It looks easy when Judy does it,'' Wendy Parkman, former Pickle Family flyer, tells the children, ''because she has practiced for hours and hours and hours. . . .''
Giggles subside. The two women pass out diabolos, and the children start taking their fun seriously. Margaret, a seven-year-old in red-striped shirt and purple sweat pants, patiently works the string of her diabolo until it finally starts to whirl and whine like a salad spinner gone wild.
What for the children is simply Saturday fun is the start of what the two women hope will evolve into a full-scale professional school devoted to the circus arts.
''There is no school like this in the United States,'' says Ms. Finelli, co-founder of the Pickle Family Circus School, which opened in January. ''There are people who teach circus techniques here and there, but no one has the same end result we have in mind.''
What they have in mind is a four-year school - much like the High School for Performing Arts in New York - where youngsters can learn the full spectrum of circus arts from a faculty of professionals. They envision a school where retired performers from all over the world can come to pass along the secrets of their craft.
The school is patterned after the renowned Moscow Circus School, where talented young Russians study circus with the same seriousness that young Americans study music or dance. ''There, circus is revered,'' says Ms. Finelli. ''It is on a par with ballet. Here, there is still that attitude that opera is one thing, but circus is quite something else.''
Judy Finelli, who has juggled on ''Sesame Street,'' in Carnegie Hall, and with the Pickles since 1982, is reputedly one of the best in the country. She taught circus techniques to acting students at New York University for 10 years and gave summer workshops at such places as the Juilliard School, the National Theater of the Deaf, and the Dell 'Arte School of Mime and Comedy in Blue Lake, Calif. Among her former students are Robin Williams, Christopher Reeve, and David Ogden Stiers. One of her greatest frustrations, however, is that none of her students ever wanted to become a circus performer, a fact she attributes to the tarnished image of circus in America.
Overcoming this prejudice is one of the goals of the school and has long been an objective of the entire Pickle Family.
Since its first performance in a San Francisco high school gym in 1975, the Pickle Family Circus has delighted audiences and critics up and down the West Coast, through the Southwest, and in London with its joyful blend of traditional circus and American vaudeville. The first show was funded with some of the first CETA (Comprehensive Employment and Training Act) money available for performing artists, and the company remains a nonprofit organization supported in part by grants from the California Arts Council, the San Francisco Hotel Tax, and the National Endowment for the Arts.
Founded by Larry Pisoni (also known as ''Lorenzo Pickle,'' the circus's patriarchal red-nosed clown) and his wife, Peggy Snider, both former members of the San Francisco Mime Troupe, the circus is a throwback to the one-ring circus of Europe. That many of the Pickles were once street performers is no coincidence: The performers quickly establish an intimacy with their audiences and encourage children to sit near the ring. Top-notch clowning is an important part of each show, and a professional jazz band accompanies each performance.
Unlike the American three-ring circus, the Pickle Family Circus includes neither production numbers nor elephants. The closest thing it has to an animal act is a chorus line of dancing gorillas, which are actually humans in disguise.
The Pickle Family Circus has long held ties to the alternative theater that developed in the San Francisco Bay Area in the '60s and early '70s. But unlike many of the troupes, the Pickles express their politics in style rather than content.
Their first show was presented to benefit a child-care consortium in a lower-class neighborhood. Since then, the bulk of their shows have been cooperative efforts in partnership with community-based service groups. Last year the Pickles helped their community group sponsors raise over $100,000. They often bring their shows to small rural communities where live theater, not to mention good jazz, is an unaccustomed treat.
''We're a '60s phenomenon that managed to survive to the '80s,'' says Wendy Parkman. The show has no stars, and all of the performers do double or triple duty - acrobats juggle, jugglers clown, clowns tumble, and they all put up and take down the bleachers.
Mrs. Parkman, who holds a degree in drama and dance from Sarah Lawrence College, began performing on the streets of San Francisco with a juggling troupe called ''The Bay City Reds.'' She joined the Pickles as an acrobat in 1979, and a year later, at the age of 31, made her debut on the trapeze. Her aerial act - 30 feet up, without a net - caused one London reviewer to write, ''It is quite hard not to shut your eyes and send up prayers for her survival.''
Back in the class, the high point (literally) comes when Wendy Parkman once again assumes the role of the beautiful lady on the flying trapeze. The awestruck children wait breathlessly as she gracefully slides her legs up the inside of the red velvet ropes of the trapeze, then hangs upside down by her knees in the classic ''catcher's lock.''
''OK,'' she grins, her hands dangling free. ''Who wants to be first?''