MUSIC REVIEW : Pasternack Shines in Substitute Role With Pacific : The pianist, on less than two day’s notice, comes from Boston to give a confident, forceful performance with all the heroic flourishes.

At least it wasn’t business as usual at Segerstrom Hall Wednesday night.

The Pacific Symphony’s ever-dynamic conductor, Carl St.Clair, had put together an unusual program--Mendelssohn’s First Piano Concerto as an opener, Beethoven’s platypusian Choral Fantasy in the concerto spot, and Maurice Durufle’s mellow Requiem as a closer--only to have his double-duty piano soloist, Norman Krieger, call in sick. Where to find a pianist, on less than two days notice, with both works in his fingers?

From Boston, Benjamin Pasternack, winner of the 1988 Busoni Competition, was procured. He had done this before. In 1988, he came to the rescue of the Boston Symphony on less than 36 hours notice--significantly, for the same conductor.

Pasternack already had the familiar Mendelssohn in his repertoire. He tore into the piece with expected crispness and unexpected but welcome brashness. He brought point to the acrobatic passage work; in the Andante, he provided suitably casual poetics. St.Clair and company supported with enthusiasm and finesse.

With music and page turner in tow, Pasternack was, it appeared, not as familiar with the “Choral Fantasy.” Nevertheless, a few botches aside, he gave a confident and forceful rendering with all the properly heroic flourishes. He left room for some further interpretive polish but these would be minor doings.

The orchestra accompanied with verve, and momentary patches of ensemble untidiness. The Pacific Chorale made a huge, well focused sound at the end.

Under the circumstances, Durufle’s Requiem seemed anticlimactic, but then maybe it always does. Unlike most gloom and doom requiems, Durufle’s piece depicts a kinder and gentler death, clouds, angels, tranquillity, Elysian fields, that sort of nonsense.

To be sure, there are some grandiose moments, and St.Clair made the most of them in big, roaring yet surely balanced climaxes. For the rest, sans baton, he molded the Gregorian lines persuasively, blended colors knowingly, shaped episodes expertly. Still, it seemed Andante ad infinitum . One gets the point with this piece rather quickly.

Baritone Robin Buck sang his brief offerings clearly and expressively. Contralto Lyria Pegram sounded not completely in control of her large instrument but brought appropriate fervor to the Pie Jesu .

The Pacific Chorale floated or shouted, as necessary, keenly balanced, rhythmically cohesive and nicely tuned all the while, managing an extra shimmer in pianissimo passages. The orchestra produced clear textures, unassuming detail and impressively muscular heights without ever overpowering the choir. Berlioz’s Requiem, anyone?