Combine the barn-raising traditions of Maine and California experimental theater, and the end product is a burgeoning movement of build-it-together playgrounds led by architect Bob Leathers.

The multilevel wooden structures featuring mazes, slides, bridges and tunnels are built by parents in an average of four days, usually beginning on a Thursday morning and culminating in a Sunday-evening celebration. Leathers, of Ithaca, N.Y., provides the design and supervises the volunteer construction workers who can total over 400 in one weekend.

About 70 "creative play areas" have been constructed out of telephone poles, 2-by-4s, tires and barrels by community groups from Virginia to Upper State New York under Leathers' watchful eye.

The concept of designing elaborate play structures and then turning the actual construction over to parents, not all of whom qualify for the semiskilled crews, was born of Leathers' "innate belief in people's ability to do things."

"As a child in Maine we had great faith in the success of grass-roots efforts. It was a do-it-by-the-seat-of-your-pants kind of thing."

The visionary aspect of tapping children's fantasies and then translating them into child-scaled structures evolved from Leathers' years of producing "happenings" on the West Coast during the '60s. As a graduate of the Rhode Island School of Design, Leathers spent his days designing $13-million office complexes and his after-hours creating light shows and other "imaginary environments" for California's Crystal Theater.

"Every production was like an impossible dream, but after seeing it work enough times, you began to believe it can happen. It is the same with the playgrounds. Each one is different and each is the realization of the dreams of the children and the parents who build them."

The process of building a playground begins with a series of roundtable discussions between Leathers and the children. They are the experts, he believes, and his designs while recognizably similar, also are unique to each school. The children's "wishlist"--a curly slide, a castle with a dungeon, a maze--are taken to the teachers and parents who will decide how and what they can build.

Last fall, children at Navy Elementary School in Fairfax said they not only wanted a castle, they also wanted a dragon to guard the gates. At the parents' meeting, one father offered to donate a 3,000-pound tree trunk, which two other fathers spent three days carving with chain saws.

"These were guys who had only used chain saws to cut firewood," says Leathers, "but together we created a dragon with step-like scales up his back out of a 12-foot log."

Again and again Leathers, 40, hears requests for "little cubbies" or a "tower with little rooms."

"Kids like spaces scaled to their size," says Leathers. "They live in an adult world and they want a space that is theirs."

Some schools, such as the Key Center for handicapped children in Alexandria, present a special challenge. In a recent planning session prior to a November building date, teachers and parents hashed over the mechanics of a wheelchair swing; how to include a backboard wall and avoid a watch-teacher-retrieve-the-ball-from-the-other-side-of-the-fence game; and how to design a vandal-proof "car wash" for wheelchairs with streamers and other sensory stimuli.

By approaching each school with a "what-would-you-like?" openness, Leathers receives new ideas and modifications continually, so that each playground is an improvement over others preceding it.

Leathers has been asked to incorporate his ideas into a book, but the concepts of what makes a playground work are so in flux, he says he can't pin them down for print. "This is something that is constantly evolving. I don't expect to ever produce the perfect design but to keep changing the design as we discover new systems."

Leathers' expertise in playground design evolved almost by accident. Twelve years ago he was asked to design a playground at his own child's school which resulted in 15 weekends of parent labor and the prototype for later designs. Three years later when another school principal asked for a design, Leathers' first response was, "I don't do playgrounds. I am an architect." He was persuaded, however, and that project took only 10 weekends. Within another five years he had designed about a dozen playgrounds in his hometown area, and is now considering projects as far away as New Mexico and West Berlin.

"This is really just a hobby--something I do on the side," insists Leathers, whose architectural firm designs single and multifamily housing and human-services buildings. He sets a limit of 25 playgrounds a year and is already half booked for 1983.

"Designing creative play areas is a great fullfilment for me," he says. "It tests me designwise because these are very intricate structures. It also provides an outlet for community action in the organization of hundreds of people, and then seeing them accomplish something they never dreamed they could."