The National Symphony Orchestra played to a full house last night at the Kennedy Center -- and to quite a sophisticated one. The American Symphony Orchestra League, the leading service organization in its field, is holding its annual convention in Washington right now, meaning that there probably are as many managers, music publishers, public relations directors, critics and artists' representatives wandering the streets of Northwest as there usually are lobbyists and lawyers.

And what did our visitors hear last night? NSO Music Director Leonard Slatkin and his forces offered a fairly representative sampling of their programming -- some admirable, slightly neglected 20th-century music (Paul Hindemith's Symphony "Mathis der Maler"), one out-and-out warhorse (Elgar's Variations on an Original Theme, better known as the "Enigma Variations") and an amiable piece by a living American composer, Mark O'Connor's Double Concerto for Two Violins and Orchestra, with the solo parts played by O'Connor and Nadja Salerno-Sonnenberg.

Let's start with the concerto, which impressed me as light music of an unusually high order, the sort of piece that in the years to come will likely fill symphonic pops programs, should that particular institution continue. O'Connor's concerto, written in 1997, is in three movements -- fast-slow-fast -- and combines a sort of swing blues with jazz vamps and a near-minimalist stasis (was anybody else reminded of John Adams's "Shaker Loops"?).

Surprisingly, Salerno-Sonnenberg's playing had more country twang than O'Connor's did, but both are wonderfully fluent fiddlers and they seemed to be having a very good time together. The piece is purest fluff, but it is very good fluff; it sets out to entertain, and it does, pretty steadily, for more than half an hour. If this sounds like damnation with faint praise, I don't mean it that way -- better to set a modest goal and fulfill it, making some people happy in the process, than to strain for masterpiece status, never bringing anybody else along.

The program began with a nuanced, energetic rendition of the Hindemith symphony -- an ambitious work that is notable for the way it combines clarity and density, two qualities that rarely manage to coexist. Hindemith was proud that he never wrote a single note in any of his pieces that he could not physically play himself (which might explain why the piano music in his Tuba Sonata is so much more difficult than the music he accorded to the "star" instrument), and there are moments when one suspects that he placed a greater emphasis on competence and industry than inspiration. Still, his busyness generally keeps one's attention, and the piece proved a terrific workout for the NSO's lower brass.

Slatkin has a rare affinity for the music of Edward Elgar, and it was good to hear the "Enigma Variations" played so lovingly. (I confess that I usually find myself waiting eagerly for the bejeweled "Nimrod" Variation throughout most of any "Enigma" performance and then wishing I could hear it again the moment it is over.) One of Slatkin's great gifts is his sense of musical proportion, and he built this performance in a long arc, giving each variation its due ("Nimrod" taken very slowly, in grave and exalted wonderment) yet managing to yoke them all together. Last night, the "Enigma Variations" sounded like a first cousin of the Brahms "Haydn Variations" -- and all the better for it.

The program will be repeated tonight and Saturday night at 8.

Mark O'Connor played violin in his concerto.He was joined by Nadja Salerno-Sonnenberg.Slatkin showed off the NSO to the visiting crowd.