MEDIOCRE MUSIC poses a major challenge to performers. It takes a special sense of drams and dash to transform a collection of second rate ideas into a satisfying, enjoyable performance. Last Friday, violinist Lynn Chang and the HRO showed just how it is done in a riveting performance of the Sibelius Violin Concerto.

Apart from a lovely opening melody this piece exemplifies the self-indulgent bombast of many last-Romantic works. It has become popular as a showcase for virtuosos, however, creating excitement and interest through unrelenting technical demands.

Chang played with an effortless agility that minimized the ponderousness of the material. The sense of struggle that usually accompanies a performance of such a difficult piece was all but lost as Chang dashed through scale passages and tossed off finger-breaking double stops with remarkable case. He didn't display a particularly rich, sweet tone or dwell on dramatic musical events, but his performance was thoughtfully conceived and carried out with such energy that the audience was swept headlong over the dross.

The orchestra, which provided solid support for Chang under the clear direction of Dr. Yannatos, began the program with a mediocre work of their won--Men and Mountains by Carl Ruggles. His works get played when patriotic programmers want to include something distinctively American. But even a Blake reference in the title and occasional moments of lyric beauty in the second movement cannot salvage this work. Fortunately it is short and gave the orchestra a chance to warm up and demonstrate its find symphonic sound.

IN THE INTEREST of musical merit, Brahms's Fourth Symphony comprised the second half of the program. Flaws of intonation and ensemble marred the HRO's performance of this difficult standard work. But these were easily forgiven in the context of the HRO's energetic and enthusiastic playing. Dr. Yannatos never let the playing degenerate into a well-intentioned shambles, but firmly structured this potentially unwieldy masterpiece.

In even a poor performance of Brahms's Fourth, which this was not, there is still Brahms's music to admire. The value of the Sibelius, however, depends largely on the performance; the music cannot supply the necessary coherence and drive. Through their artistic labor, Chang and the HRO created an overwhelming sense of value" where little might have existed.