Roy Gean and Tensia Fonseca, directors of Maryland School of the Ballet in Bethesda, measure their success by their losses.

If their teaching has been effective, say the directors, they lose their students to professional ballet companies, which is exactly what they want to do. By that measure, the 12-year-old school has been remarkably successful, primarily, as Gean says, because the directors have worked "very, very hard."

"Tensia and I are willing to do anything," Gean said. "We have cleaned floors, sewn costumes, washed out tights after every performance, is ironed costumes after every performance . . ."

Teaching and running the ballet school and its affiliate company, the Maryland Youth Ballet, sometimes can mean long hours. "Sometimes," said Gean, "when we've been preparing for a production, I've worked until four in the morning and then come right back at seven to work through the day."

Gean and Fonseca trained as dancers and were members of several professional companies before opening their school. Gean danced with the Washington Ballet, the National Ballet and the Mannheim Opera Ballet. Fonseca was a member of the national company of Costa Rica, her native country and studied in the U.S. with Andre Eglevsky. She turned down an offer from the American Ballet Theater and got married instead.

She and Gean met in 1965 and decided to form a ballet school with the goal of training dancers from their earliest years through acceptance to major dance companies. For five years neither accepted a salary; all their money and energy went into making the school work.

One of the their earliest projects, building a dance floor for the school, reflects the ingredients they have used to make the school a success: committment, hard work, knowledge and attention to detail. Neither had any experience in building a floor, but they put it together in three, 12-hour days at $1,400 less than a workman's estimate. And they built the floor so well, giving it that special spring dancers need, that they say several professionals have praised it.

So far nine dancers from the Maryland Youth Ballet have joined professional companies; 42 students have received scholarships to ballet schools in New York City, and two early graduates, Cheryl Yeager and Fonseca's son, Peter Fonseca, and members of the Amercian Ballet Theater.

Fonseca and Gean say their program stresses cooperation and support as well as artistic excellence. "If they want to see me really, really angry," said Fonseca, "the girls know that all they have to do is show some jealousy of one another."

And both insist that parents become involved in the school and share the commitment being a dancer requires. "Without support from the parents a student can never make it," said Fonseca.

She and Gean believe their own willingness to work has made the parents more interested in helping. For example, one father took a leave from his job and worked 12 hours a day for two weeks to build the set for their current production. "The Enchanted Clock."

The production, which opened yesterday at Walter Johnson High Schol in Bethesda, is the Youth Ballet's holiday production.This year's production will run through tomorrow with performances at 2 p.m. and 8 p.m. each day and a special New Year's Eve matinee. (For ticket information call 657-4253 or 654-9547).

Fonseca and her son choreographed "The Enchanted Clock" to the music of Shostakovich and Kabalevsky. The story, in three acts, begins in a mountain village where there is only one clock. The clock stops when gypsies cast a spell to free Kokolin, the spirit of the clock. Since the clock has never before stopped, no one in the village knows how to fix it. The rest of the story revolves about the visit of the townspeople and their children to the Land of Lady Time, who possesses the magic to fix the clock.

To give their dancers more experience performing under professional conditions, Gean and Fonseca have taken the Youth Ballet on tours of Central America twice, once in 1973 and again last summer.On both tours the dancers (in 1977 the youngest was nine) performed before sold-out houses. The income from the 1977 tour was given to Central American groups to support local arts.

Fonseca and Gean said invitations from Central American cultural ministers for another tour next year are under consideration.

Despite triumphs, both directors find room for improvement.

"We're always looking for ways that we could be better," Gean said. "The only time we feel satisfied is when one of our students gets a professional contract and that's a momentary thrill. The next day we're back, working on our problems."