Washington celebrates Labor day weekend the way most places do: a few people labor and a lot of people play. For instance, tours will be given this Monday at the WHITE HOUSE (normally closed on Mondays), 10 to noon; for tickets, go to the kiosk on the Ellipse south of the White House. The WASHINGTON MONUMENT will be open too, for trips to the top from 8 till midnight. Free.

At the Smithsonians, the NATIONAL AIR AND SPACE MUSEUM begins its September tours this Saturday at noon, focusing on Howard Hughes as pilot, designer and inventor. Tours continue Thursdays and Saturdays through September; meet at the tour desk in the Milestones of Flight gallery. Also at the museum Saturday is a talk in the Albert Einstein Spacearium, this month discussing famous telescopes in history. Free, Saturday at 10.

Outside on the Mall is the FRISBEE FESTIVAL, Sunday noon to 5. It's non-competitive and there'll be champions and instructors giving workshops as well as showing off. Free; rain date, Monday.

The NATIONAL MUSEUM OF AMERICAN HISTORY celebrates Thomas Edison's bright idea Saturday with 3,000 balloons, all shaped like light bulbs and distributed in the Hall of Electricity (on the first floor of the Museum) at 14th and Constitution NW. Free. Saturday at 2, there's a free concert in the Hall of Musical Instruments: Laurie Andres plays country dance music from America, Ireland, England and Scotland.

The NATIONAL ZOO is open every day this weekend, 8 to 8 (housed exhibits are 10 to 6). Films showing at 10:30 and 4:30 in the Education Building include an overview of the zoo and one about the pandas. All free; parking is $2 at 3000 Connecticut Avenue NW. Phone: 673-4717.

To commemorate the Irish labor that helped build it, the C&O CANAL will be reeling on Monday with Irish dancing and music by 10 groups who'll perform noon to 6. Performers include the Peggy O'Neill Dancers, the Hags and Celtic Tradition at the Foundry Mall in Georgetown, between Jefferson and 30th streets (below M).

At MERIDIAN HILL, there'll be a walk and talk featuring the park, Washington's oldest, Saturday at 10. For information and directions call 426-6829.

The WJLA TV-7 fishing derby continues, one of the reasons for the WATERFRONT FESTIVAL going on around it. The contest ends Sunday (prizes are awarded Monday at 3) and there's music at 2 and 4 Saturday, Sunday and Monday, while arts and crafts are for show and sale noon to 6. Free. Further fishing can be had at the mountain trout fishing pond, a 50-foot pool stocked with trout in which you can fish for seven minutes for $1. Prizes awarded every two hours for the largest catch. All on Water Street between Seventh and Ninth streets SW.

For those skippers who haven't won a race in the last 12 months, now's your chance to go out in a big way: take a ribbon at Monday's ALSO-RAN REGATTA, running 10 to 4. For cruising and sailboats, the race is just off the parkway near National Airport at the Washington Sailing Marina (off George Washington Parkway north of Alexandria). Pre- register at the marina Saturday and Sunday, noon to 4, and 8:30 to 9:30 Monday. For information call 683-3182 evenings.

Other goings-on around town:

PET AWARENESS DAY at Carter Barron, Saturday noon to 4, is a chance to take bowser out for some excitement -- as long as he's adult and healthy, restrained and on a leash, please. Sponsored by the Pet Owners Association of Metropolitan Washington, it's a gathering to promote responsible pet ownership, and the guests of honor can compete for such titles as "Pet/Owner Lookalike," "Ugliest Dog" or "Rarest Breed." Free at 16th and Kennedy streets NW. For more information call 829-2700.

A live JAZZ DANCE CABARET this Sunday at 10 p.m. serenades the end of summer: Tickets are $10 for the WPFW- sponsored party featuring Nap Turner, Mary Jefferson and the Charlie Hampton Quartet. At St. Benedict the Moor Hall, 320 21st Street NE. Call 783-3100.

A marathon SINGLES SQUARE DANCE starts with registration at the Capital Hilton Friday at 9 a.m. Dancing starts at 10 and continues through the final dance Sunday night at 11. A RECORD CONVENTION turns the tables this Saturday at the Holiday Inn in Crystal City. Its subtitle tells it all: the "Rock and Roll Flea Market" is 9 to 4:30, admission is $2. At U.S. 1 and 15th Street.