The 20th International Children's Festival opens Saturday for three days and is expected to bring 35,000 people to Wolf Trap Farm Park, making it the biggest event for young people in the metropolitan area.

"You don't have to speak the language to enjoy dance and performances from other cultures," said Toni McMahon, president of the Fairfax County Council of the Arts, a sponsor of the festival. "There's an international language of the arts."

This year's festival showcases entertainment by young people from Bulgaria, Colombia, Costa Rica, Puerto Rico and Taiwan. Performers from around the country also will be featured. Bob McGrath, from television's "Sesame Street," will host the festival.

Hands-on workshops for children ages 3 to 12 will have crafts from North, Central and South America. Sign-language interpreters will be on hand to assist with the workshops and performances. "Kids interact with each other and adults interact with the kids," McMahon said. "It's not TV or a video, it's reality."

Beginning this year, the festival's new Foreign Relations Committee has initiated a five-year plan dividing the globe into five regions. This summer's theme is "The Americas, A Rainbow of Colors."

Performances and activities from the Soviet Union, Eastern Europe and Southwest Asia will be highlighted in 1991; Europe in 1992; Africa in 1993; and Asia, Australia and the South Pacific in 1994.

"You can read about or see pictures of other countries, but if you meet and talk to the people and watch their art forms, it becomes real," McMahon said.

This weekend, the festival's Special Guest program will enable 2,864 homeless people and other disadvantaged Virginia, Maryland and District residents to visit the festival. Area businesses will provide participants with food, transportation and vouchers for souvenirs.

The festival began in 1971, when Joan Blair, Catherine Filene Shouse and Christina Heimlich conceived the idea of a theater festival for children. The program would be held at Wolf Trap, which Shouse recently had donated to the National Park Service.

"Mrs. Shouse would come and see rehearsals," said Heimlich, a 35-year resident of Falls Church whose Christina Heimlich Dancers have performed at the festival every year since its inception. " 'Don't you think it will make children happy?' she asked. And I said, 'Indeed it will.' But no one knew it would develop in such a big way."

The first International Children's Day had 400 performers and an audience of 700. The festival has grown substantially over the past 20 years.

The festival doesn't end with Labor Day. Since 1987, the performers from abroad have been invited to stay for a few days to visit students in Fairfax County schools.

"Students have an opportunity to see the many ways that they share the same goals and interests, like family and schools," said John Tozzi, chairman of the festival's Education Exchange Committee. "They have an opportunity to care about each other because they get to know one another."

The students sent typical American items, including candy wrappers and theater tickets, to their foreign peers last spring to prepare for their meeting.

On Wednesday and Thursday, performers from Taiwan will visit students in McLean; Costa Rican youngsters will see students in Chantilly and Herndon; Colombian performers will visit "They have an opportunity to care about each other . . . ."

-- John Tozzi

students in Fairfax; and Bulgarian performers will meet young people from Fairfax and Clifton.

"It's really exciting for all these students to have a chance to share how they are both alike and different," Tozzi said. "They build good bonds that help international understanding."

The festival runs from 10 a.m. to 4:30 p.m. Saturday, Sunday and Monday at Wolf Trap, rain or shine. Tickets are available through the council or the Filene Center box office. Admission is $8 for adults and $6 for children ages 3 to 12 and for senior citizens. Children younger than 3 are admitted free. For information, call 642-0862.