Conducting and composing would seem to go hand in hand, but few have succeeded at being equally proficient at both. Certainly Gustav Mahler and Leonard Bernstein jump out, but far more negative examples come to mind.

Beyond directing their own music, most composers don't get great results, and so often the music of top conductors is learned instead of inspired.

Andre Previn is among the few who have succeeded in making the transition from the podium to the pen and it was on display last night at Heinz Hall in his first appearance here in four years.

Once primarily known for his performing and his directorship of ensembles such as the Pittsburgh Symphony Orchestra and the London Symphony, his compositions are now held in higher esteem. With his opera "A Streetcar Named Desire," a violin concerto and numerous songs, he has a body of work that has had success.

Previn returned to lead the PSO with a new work and the audience responded with a warm welcome to the maestro who led the orchestra from 1976-84.

Previn wrote his Harp Concerto, commissioned by the PSO, for the orchestra's estimable harpist, Gretchen Van Hoesen. She plays the instrument with uncommon strength and vigor, but in this work Previn called for delicacy or lushness rather than pyrotechnics.

The orchestra writing for the three-movement piece was tonal yet discursive, as if multiple themes were bouncing around the composer's head, vying for prominence. It never grabbed me, although there were fleeting moments of lushness.

But the harp part had focus, form and substance. Beginning with an eight-note motive in the first movement, the harp dominated the piece. In fact, with two cadenzas and multiple other solos, the work almost had the feeling of a harp recital. The second, and longest, cadenza had Van Hoesen at points strumming the instrument like a grand old Romantic harp, rendering it a calliope and plucking it like a percussion instrument. Even though it did not ultimately hook me, this was the highlight of a work that did the one thing a concerto must -- celebrate the instrument.

Truth be told, part of the shift of Previn's reputation stems from the fact that he simply isn't conducting with the same vigor and precision as he once did. The suite from Copland's magnificent "Appalachian Spring" had delicate moments, such as the aching nostalgia of the first theme, but sagged in the middle. The famed variations on "Simple Gifts" should build with more tension.

The musicians sounded enervated in Beethoven's Fourth Symphony, and again the best moment came quietly: Clarinetist Michael Rusinek's solo in the second movement.