All of these parks offer package deals or discounts, so if you pay full price you have only yourself to blame. WILD WORLD -- 13710 Central Avenue, Mitchellville, Maryland (three miles east of the Beltway). About half an hour from downtown Washington. Metrobus service on Routes T10 and T11 from the Addison Road Metro station. Open 10 to 10 weekends beginning April 30, daily from Memorial Day through Labor Day, weekends through October 30. Admission $11.50 (season pass $30); senior citizens $5.75; children under four free. Group discounts. Parking $2. 249-1500 (free call from the metropolitan area). KINGS DOMINION -- Doswell, Virginia (75 miles south of Washington on I-95). Open 10 to 8 weekends through May 29, plus April 4 and May 30. Closed May 1. Open 10 to 10 daily June 2 through August 28, weekends (plus Labor Day) thereafter through October 8. Admission $13.50, children under three free; group rates. Parking $2. 804/876-5561. BUSCH GARDENS -- Williamsburg, Virginia (160 miles from Washington via I-95 south and I-64 east. Or take the U.S. 17 bypass south from Fredericksburg for an uncongested highway that passes through Tappahannock, one of Virginia's friendliest towns, and Yorktown, which is not only historic but also home to Nick's Famous Seafood Pavilion. Open weekends 10 to 7 (and Easter Monday) April 2 through May 8; daily from May 14 through Labor Day; and weekends through October 30. Admission $13.95; children under three free; evening and two-day rates and season passes; group rates; and discounts with McDonald's coupons. Parking $2. 522-1387 (free call from the Washington area). HERSHEY PARK -- Hershey, Pennsylvania (140 miles from Washington via I-270 to Frederick; U.S. 15 north to Harrisburg; and U.S. 322 east). Open the weekend of May 14-15, daily from May 21 through Labor Day, weekends through September 17. Gates open at 10; closing times vary from 6 to 10. Admission: ages nine through 61, $12.95; over 62, $6.95; five through eight, $9.95. Special rates for afternoon and evening entry, plus group discounts. Free parking. 717/534-3916. GREAT ADVENTURE -- Jackson, New Jersey (190 miles from Washington via I-95 to exit 7A on the New Jersey Turnpike; exit 98 on the Garden State Parkway). Open daily March 31 through April 10; the weekends of April 16-17 and 23-24; daily April 29 through September 18; and weekends through October 16. Gates open at 10; closing times vary from 8 to midnight. For information on the various discounts available call 953-2411 (local call in the metropolitan area). Standard admission: combination ticket, $14.95; theme park only, $13.95; drive-through safari only, $5.25. Children under four free. Parking $1.50.