"Who says everybody in Washington leaves town over a holiday weekend?" WLTT-FM deejay Dave Arlington asked as he surveyed an estimated crowd of 50,000 that stretched before him on the grounds of the Capitol last night. The honey-voiced Arlington was on hand to play host for the first of the National Symphony's "American Festival Concerts"; the 50,000 were there to listen to the music of Brahms, Ellington and Gershwin but also to feast and revel in the balmy evening air.

Picnickers scarfed down everything from fried chicken to empanadas, and despite a ban on alcohol, the chablis and beer flowed freely. And even after the music had begun, many listeners found additional ways to amuse themselves. Trivial Pursuit games were everywhere; one woman sat engrossed in a biography of rock star Jim Morrison; another fellow read Readers' Digest. Many napped and the more romantically inclined lay tangled in each other's arms. One little girl stood conducting her own imaginary ensemble.

Up on the podium, the young conductor Andrew Litton, looking jovial and sporty in his white jacket, began the program by leading the NSO through a dynamic rendition of Brahms' Symphony No. 1. One of the composer's most popular and compelling works, this is a piece of both throbbing intensity and featherweight buoyancy. Litton set just the right tempos -- many conductors turn the first movement, particularly, into a dirge-like affair -- and gleaned from the orchestra a wonderful clarity and rhythmic precision.

After intermission came the lighter musical fare. The "Duke Ellington Fantasy" was one of those slick aural packages that chop, puree' and blend each beloved tune -- in this case, "Caravan," "Mood Indigo," "Don't Get Around Much Any More," "Sophisticated Ladies," "Take the A Train," etc. -- into one bombastic crowd-pleasing whole.

Far purer in content but every bit as high on the entertainment scale was the NSO's performance of Gershwin's "An American in Paris." The musicians captured the great oral bustle, the blowsy can-can and the bluesy refrain with considerable verve and coloration.

The audience demanded an encore, and the NSO responded with a gushing rendition of "Memory" from the hit musical "Cats." Fifty thousand people left the grounds warbling that most sentimental of melodies.