The Philadelphia orchestra has soul. No doubt about it.Trying to pin down that elusive quality, one can point to the orchestra's remarkable depth of sound, richness of blend and extraordinary unity of response. Ultimately, of the spirit projected in its playing which accounts for the orchestra's uniqueness.

Listening to the concert under guest conductor Robert Shaw at Wolf Trap Saturday night one was particularly struck by the collective sensitivity of the orchestra's members. They prepared and finished off every phrase with the smoothness of a superb athlete executing a flawless tennis stroke. There simply were no rough edges to be heard.

With the exception of Charles Griffes' "The White Peacock," the program was standard stuff - Bethoven's Sixth Symphony, Berlioz' "Roman Carnival" overture and Tchaikovsky's "Romeo and Juliet." Nonetheless, the compelling musicality of the orchestra's playing kept the listener leaning forward to follow every nuance.

The Berlioz overture began with a liquid English horn solo that led into shimmering string sounds and a golden fullness from the brass. Beet-hoven's "Pastoral Symphony" was given a broad, firmly anchored reading, marked by a deep sense of inner calm. The evocative Griffes work brought forth lovely solos from the woodwinds and some ravishingly lush sounds from the entire orchestra.

In the closing Tchaikovsky work, as in the rest of the program, Shaw conducted with a sure hand, choosing tempos wisely and pacing carefully the music's emotional flow.