To enter the Soap Box Derby:

* The derby is open to contestants aged 9 to 15. There is a $5 entry fee.

* Junior competitors must build Junior kit cars, with or without an optional fiberglass shell. Seniors may build kit cars or cars of their own design, following derby rules.

"The cost to complete a Soap Box Derby racer," says Washington area derby director Sydnee Schwartz, "will average $160-$170, without wheels." Polyurethane wheels, used in the Akron races since 1982, are $47.50 for four, including shipping.

Kits and polyurethane wheels are available from All-American Soap Box Derby Racing Products, International Soap Box Derby, P.O. Box 7233, Akron, Ohio 44306; (216) 733-8723.

Construction time, depending on the type of car built, might run anywhere from 10 hours, for a basic Junior racer with fiberglass shell, to 300 hours for a Senior racer built from scratch.

* Information, 1985 rule books, registration and order forms are available from Sydnee M. Schwartz, Derby Director, 5814 Devonshire Dr., Bethesda, Md. 20816; (301) 229-0118.

Schwartz will give a construction clinic and registration session Saturday, May 11, at Washington Gas Light Co., 6801 Industrial Rd., Springfield. The Junior division session (ages 9 to 12) runs from 10 a.m. to noon, and the Senior division (ages 11 to 15) from 1 to 3 p.m.

* Car trials will be held June 15. Cars will be inspected July 8; the Washington area derby will be run Saturday, July 13, from 10 a.m. to 4 p.m. at Eastern Avenue and Varnum Street NE. Registration deadline is May 11.

The All-American finals in Akron are set for Aug. 10.

* Those interested in sponsoring a car may contact Schwartz at (301) 229-0118 or Chuck McElroy at the Downtown Jaycees, (202) 293-0480. The Downtown Jaycees, McElroy says, "have a Youth Assistance Fund which is sponsoring several cars this year. We're looking for additional sponsorship from those individuals and local businesses interested in helping out a needy youngster."