The National Theater kicks off its fourth annual Saturday morning program for kids this weekend with a program of West African dance by African Rhythms.

Week in and week out, the quality of the free entertainment has made the National offerings immensely popular. A typical Saturday morning draws a full house of 300 for each of the two shows, at 9:30 and 11. Throughout the year, the best way to guarantee a spot is to make reservations one week in advance by calling a 24-hour phone line.

This season runs until May and features new talent and entertainment, including a production of "Hansel and Gretel," with kids from the audience becoming gingerbread cookies; an African storyteller; a Canadian jug and washboard band; and percussionist Barnett Williams, who's performed on "Saturday Night Live."

The following events are free unless otherwise noted.

NATIONAL ZOO -- Open daily; gates open from 8 to 8; animal buildings, 9 to 6; panda feedings, 11 and 3; elephant training demonstrations, 2; Sea lion training demonstrations, 2, 3001 Connecticut Ave. NW (Rock Creek Park), on the Metro Red Line. Family learning centers Zoolab and Birdlab open Friday through Sunday, noon to 3; Herplab open Wednesday through Sunday, noon to 3. 673-4717.

OXON HILL FARM -- Open daily, 8:30 to 5, Oxon Hill Road (take Beltway exit 3A, turn right on Oxon Hill Road). Saturday, 1, "Fall Flowers." Create a natural dry arrangement from wildflowers and grasses found in the pasture; bring your own vase. Sunday, 9 a.m., help a farmer with the morning chores; meet in the barnyard. 839-1177.

NATIONAL AQUARIUM -- Open daily, 9 to 5, Department of Commerce, 14th and Constitution Avenue NW. The sharks are fed Monday, Wednesday and Saturday at 2; weekday features are a touch-tank, mini- theater and a thousand types of marine life. Adults $1; children 50 cents. 377-2825.

CEDAR HILL -- Open daily, 9 to 4, 1411 W St. SE, Anacostia. Cedar Hill, Frederick Douglass' home, recalls his work with films, interpretive exhibits and a house tour. 426- 5961 or 426-5962 or 426-5963.

USS BARRY -- Open daily, 10 to 5, Washington Navy Yard, Ninth and M streets SE. The Navy destroyer's weather deck is open for public viewing and self-guided tours. 433-3377.

CHILDREN'S MUSEUM -- Monday through Saturday, 10 to 4, Sunday 1 to 4, Rose Hill Children's Museum, north of Frederick, Maryland. Take U.S. 15 north to Exit 8 to Motter Avenue; follow Motter to left onto 14th Street and left onto North Market Street, follow signs to Rose Hill. Costumed tour guides conduct tours of the 1790 mansion. Hands-on exhibits include a loom, antique toys and spinning wheel. Adults $1; under 17, free. 301/694-1646.

CAPITAL CHILDREN'S MUSEUM -- Daily, 10 to 5, 800 Third St. NE. Make a marionette with paper, glue, string and other materials. $2. 543-8600.

NATIONAL COLONIAL FARM -- Tuesday through Sunday, 10 to 5, 3400 Bryan Point Rd., Accokeek. Sunday, 9:30 a.m., "4th Annual Plantation Driving Days." Watch horse and antique carriages in driving competitions. Adults $1; children under 12, free. 301/283-2113.

RAILROAD STATION MUSEUM -- Wednesday through Saturday, 11 to 4; Sunday, noon to 5, Main Street and Maryland Avenue, Ellicott City. The renovated station has a diorama of the trip of Tom Thumb (an early 19th-century train) from Baltimore to Ellicott City. There are also sight and sound shows, model train exhibits and tours of the museum. Adults $1.25; under 13, 75 cents. 301/461-1944.

COLONIAL FARM -- Wednesday through Sunday, 10 to 4:30, Claude Moore Colonial Farm at Turkey Run, 6310 Old Georgetown Pike, McLean. Take a self-guided tour of farm life for a low-income family in Colonial Virginia. Ongoing demonstrations of agricultural and domestic chores, such as spinning and candlemaking, round out this history lesson. Adults $1; children under 12, 50 cents. 703/442-7557.

CHILDREN'S BOOKS -- Thursday and Friday, 11:30 to 4:30; Saturday, 9:30 to 1:30, Historical Society of Frederick County, 24 East Church St., Frederick, "Children's Books of Yesterday." See an exhibit of children's books dating from 1771 to 1914. 301/663- 1188.

CHILDREN'S STORY HOUR -- Friday, 3 to 4, Potomac Overlook Park Nature Center, 2845 Marcey Rd., off Military Road, Arlington. Naturalists tell stories for pre-schoolers and kindergarteners. 528-5406.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW 89.3 FM. "Galaxy Girl in the Case of the Disappearing Damsels." Follow a galactic gumshoe as she tries to crack the case of the disappearing fairytale heroines. Listeners can participate in a call-in following each program by calling 783-3104.

SATURDAY MORNING AT THE NATIONAL -- Saturday, 9:30 and 11, Helen Hayes Gallery, National Theater, "African Rhythms." Whirling dancers in authentic costume perform to traditional African music. Reservations recommended. Call 783-3372, 24 hours a day.

KIDS' DOG SHOW -- Saturday, 10 to 1, Burke Lake Park, 7315 Ox Rd., Fairfax Station, Va. (take I-66 west to Rte. 123 south which becomes Ox Road; park entrance is approximately five miles on the left). Kids ages four to 12 may enter their dogs (six months or older) in a variety of categories including largest, smallest, best trick, best behaved, friendliest and best costume; awards given. Pre-registration is encouraged, though you can register the day of the show from 10 to 10:30. $2 per dog. 323-6601.

CASTING CLINIC -- Saturday, 10 to noon, Long Branch Nature Center, 625 S. Carlin Springs Rd., Arlington. Join the National Capital Casting Club for a demonstration and clinic on fly spinning and bait casting; for kids 11 and up (under 15 must be accompanied by parent). Reservations required. 845-640.

FITNESS AND FUN FESTIVAL -- Saturday, 11 to 6:30, Hechinger Mall, corner of Maryland and Benning Road NE. A festival for kids including health screening tests, tennis and basketball clinics (with former Bullet All- Stars Bob Dandridge and Phil Chenier), games, balloon rides, puppet shows, children's fingerprinting and much more. 341-0530 or 341-0429.

OLD POST OFFICE -- Saturday, noon, The Pavilion, 1100 Pennsylvania Ave. NW. Sarah Ewing returns for an hour of miming and clowning around. 289-4224.

STORYTELLING -- Saturday, 12:30 p.m., National Museum of African Art, 318 A St. NE, "Storytelling: Igbo Folktales." Experienced storytellers recount lore and history of the Igbo people of southeastern Nigeria. 357-2700.

CHILDREN'S PLANETARIUM -- Saturday and Sunday, 1 and 4, Rock Creek Nature Center, 5200 Glover Rd. NW. First show for children four to seven (must be accompanied by an adult); second show for ages seven and up. No latecomers are admitted. 426-6829.

ADVENTURE THEATER -- Saturday and Sunday, 1:30 and 3:30, Adventure Theater, Glen Echo Park, Glen Echo. "The Stone That Sings." A story in which the audience must make decisions to affect the outcome. $3, group rates available. 320-5331 weekdays and performance days from 10 to 2.

BOYS AND GIRLS PICNIC -- Sunday, noon to 5, 3265 S St. NW, (off Wisconsin Avenue), "Annual Jelleff Boys and Girls Picnic." An afternoon of fun including an athletic tournament, swim competition, gong show, prizes, food, clowns, balloons, raffle and more. $1.50 admission for non-members. 232-1876 or 337-5753.

BLUE SKY PUPPETS -- Sunday, 2, Rock Creek Nature Center, 5200 Glover Rd. NW, "Lights Out on the Bunny Brothers." A 45- minute presentation featuring singalong, music and puppet show relying on audience participation. 426-6829.