Alexandria has a very old park and a pretty new one, and both of them will be offering free concerts and shows all summer long.

Fort Ward makes a great park for the same reason it made a great fort: It towers over the town. Which also makes it cool and breezy after sundown.

Waterfront Park, established after the city suddenly remembered that easy access to the Potomac was the original reason for its existence, is a grassy relief from the lovely but confining streets of Old Town.

A blanket and a picnic basket are de rigueur for either entertainment series. FORT WARD PARK At 4301 Braddock Road (838-4848). All performances begin at 7:45 p.m. JUNE 30 -- The Jazzmasters. JULY 7 -- New Century Singers (show tunes and traditional). JULY 14 -- Blue Ridge Travelers (bluegrass). JULY 21 -- Raggedy Grass (bluegrass). JULY 28 -- Mac Bogert on guitar (folk singer). AUGUST 4 -- Kaleidoscope Jazz Ensemble (big-band music). AUGUST 11 -- Jon Spellman's Talkin' Tales (especially for children). AUGUST 18 -- Bobby's Studio of Dance (tap, modern, Hawaiian). AUGUST 25 -- Alexandria Harmonizers (barbershop, 90 voicees). SEPTEMBER 1 -- MilPerCen (patriotic musical program). SEPTEMBER 8 -- Scottish Country Dancers and the Alexandria Pipes and Drums. WATERFRONT PARK Between King and Prince streets by the river. All performances begin at 7:30. (838-4343). Concerts cosponsored by Record and Tape Ltd. JULY 11 -- Crosscurrent (light rock). JULY 18 -- Kaleidoscope Jazz Ensemble (big-band music). JULY 25 -- Second Story (folk duo). AUGUST 1 -- Jazzmasters. AUGUST 8 -- Explore Jazz (experimental). AUGUST 15 -- Bob Lewis Orchestra (jazz and contemporary). AUGUST 22 -- Willow (light rock, lots of '60s songs). AUGUST 29 -- Blue Ridge Travelers (bluegrass). EXTRA ADDED ATTRACTION On July 9 at 7 at Chinquapin Park, 3210 King Street, Alexandria celebrates its birthday and America's with entertainment, activities for kids, food for sale, and, finally, more fireworks for folks who didn't get enough of them over the Fourth of July weekend.