Yo-Yo Ma is the ultimate responsible musician. His appearances with the National Symphony Orchestra this past weekend could have been limited to repeat performances of a single, popular concerto. Instead, he opted for two separate programs, entirely different, and both devoted mostly to contemporary compositions. It amounted to a two-day cello festival, and an overview of good-natured, not-too-aggressive art music, circa today.

The two programs were cleverly put together, especially the choice to open each evening with a work that features extensive group cello playing. On Friday night, the prelude was Arvo Part's "Fratres," scored for 12 cellos. Why 12 cellos, when the very bare-bones piece could easily be scored for three, or even two? Twelve is the standard complement of symphony cello sections, but the real reason may be the thickening of sound, a gimmick of sorts meant to boost the intensity of the very simple musical elements. It produces a dark and melancholy sound, which, combined with repetition, is hypnotic. But it has an air of falsity, as if Part has simply turned up the "Ethereal" knob on the stereo.

Ma has actively worked to build new repertoire for his instrument and his superstar status gives him leeway to make new works a regular staple of his performances. He succeeds because audiences trust him and because he is an exceptional musician who rarely, if ever, performs with less than complete commitment. His tone is trademarkable, his physical presence reassuringly expressive, and he smiles.

John Williams's newly revised Concerto for Cello and Orchestra is not a bad work at all, despite expectations of Hollywood schlock raised by his film scores. In fact, the concerto is a deft and ultimately moving manipulation of many different styles and sounds. The brass chords of Messiaen's "Turingalila" Symphony, orchestral textures reminiscent of Szymanowski, references to Elgar and others, all make appearances.

Ma offered the cohesive element. In the Williams, and later Dvorak's Cello Concerto, he took the role of romantic poet, a Byronesque brilliance that is both heroic and deeply, powerfully introspective. Leonard Slatkin conducted the orchestra with precision in the Williams and real fire in the Dvorak.

CAPTION: Yo-Yo Ma makes new works--such as the John Williams piece he played Friday--a regular staple.