BARBER: "CAPRICORN" CONCERTO; ESSAY NO. 1. COPLAND: "SAGA OF THE PRAIRIES"; "AN OUTDOOR OVERTURE." IVES: OVERTURE FROM THIRD ORCHESTRAL SET. Pacific Symphony conducted by Keith Clark. Varese-Sarabande VCD-47211 (compact disc). With catalogue deletions escalating by the week, this astutely planned collection of conservative Americana fills an urgent need right now, though listeners will question the inclusion of the Ives, left uncompleted at the composer's death and sympathetically reconstructed by David Porter. Clark brings a welcome brio to the buoyant extroversion of the Overture and "Saga" (aka "Music for Radio") and a canny feeling for form and detail to Barber's underrated 1944 concerto grosso--the adept soloists, listed in small print, are Louise di Tullio, flute; Allan Vogel, oboe, and Anthony Plog, trumpet. Varese provides an agreeably natural acoustic with intelligent pinpointing of solo contributions.