Thousands of youngsters are expected to blanket Wolf Trap Farm Park this weekend for a children's performing arts festival that will feature storytellers, dancers, puppeteers and magicians. Among the acts are 29 from Maryland.

Organizers of the 15th annual International Children's Festival expect as many as 20,000 people to attend the cultural arts celebration, which will include young talent from 21 states and 24 countries. Modern American, Greek, Indian and African dances will be performed, and gymnasts, mimes and singers are also expected. More than 1,300 performers, many between 6 and 19, will participate.

Local auditions for this year's festival were held last spring at Fairfax High School. Twelve panelists judged performances on family appeal, quality, stage presence, educational value and potential for audience participation. Out-of-town groups sent videotapes of their proposed routines.

The international festival is sponsored by the Fairfax County Council of the Arts, a private, nonprofit organization that produces cultural programs throughout the county. Council officials expect to raise $90,000 this year, two-thirds of which will cover operating costs.

The festival will be held from 11 a.m. to 4 p.m. Saturday, Sunday and Monday. Wolf Trap is located off Rte. 7, four miles west of I-495. Admission is $5 for teen-agers and adults, $3.50 for children aged 4 to 12 and free for those under 4.