On an anxious and unsettled evening for the National Symphony Orchestra (the ensemble's beloved music director emeritus Mstislav Rostropovich is in a Moscow hospital, battling cancer) a relatively new figure on the scene, principal guest conductor Ivan Fischer, took the stage of the Kennedy Center last night and reaffirmed the NSO's importance in our musical life.

If the rumors are true -- and such matters always remain open questions until the ink on a contract has dried -- Fischer may soon be appointed the sixth music director in the NSO's 76-year history. On the evidence of last night's program and some fine recordings, he would seem a thoughtful, capable and altogether worthy candidate for the position. There was nothing fancy about his musicmaking last night -- no grand displays of temperament, no podium heroics, no showboating whatsoever -- but there was also nothing that was cheap or less than fully serious.

Ivan Fischer might become the National Symphony's new music director. (Nso)

The program was devoted entirely to music by the unfathomably unfashionable Felix Mendelssohn -- the Symphony No. 1 in C Minor, Op. 11, and the music from "A Midsummer Night's Dream." The first piece was finished when Mendelssohn was 15, and the Prelude to the "Midsummer" music was undertaken the following year.

One of the hoariest cliches in what the critic and composer Virgil Thomson used to call the "music appreciation racket" has it that Mendelssohn was "born a genius and died a talent." That Mendelssohn wrote undeniably great music at an earlier age than any other composer -- yes, even earlier than Mozart -- is easily proven by listening to the extraordinary Octet, one of the few perfect pieces in the repertory and the creation of a 17-year-old boy. But it seems to me that the later Mendelssohn has always gotten a bad rap, and that much of the music he wrote past the age of consent has been consistently undervalued.

The reason, I think, is the composer's frank conservatism: In the past century or so, we have placed a high premium on radicalism, and Mendelssohn offers us very little of that. Instead, even as a teenager, he writes like a charming, youthful but very distinguished Oxford don -- all t's crossed, all i's dotted. The Symphony No. 1, which began the program last night, was finished after Beethoven's Symphony No. 9 had already been performed and changed the world, but it harkens back to Haydn. If you like, Mendelssohn might be considered the first, and one of the greatest, of all "neoclassicists."

Within its self-proclaimed limits, the symphony is very beautiful music, both rustic and sophisticated, shot through with a mixture of youthful passion and serene technical mastery. Fischer's direction was vibrant, alert, interested and always deeply responsive.

Even better was the music from "A Midsummer Night's Dream" -- not just the Prelude but the 12 movements that follow, created some 16 years after the Overture, when, according to customary wisdom, Mendelssohn's "genius" had given way to "talent."

It certainly didn't sound that way last night. On the contrary, the famous "Wedding March" sounded as jubilant, headstrong and celebratory as ever. The delicate, gossamer writing for chorus and soloists (here the women of the University of Maryland Concert Choir, soprano Carolyn Betty and mezzo-soprano Judith Norton) was etched and elegant, and the entire work seemed to emanate from a single impulse, however long delayed.

The NSO deserves a music director who will take the job seriously, who will drill the orchestra until it delivers its best efforts, who will place an emphasis on genuine music-making instead of flash and tinsel. There were some flubs last night -- right now, the group sounds as though it could use a full-body workout -- but the spirit was there, and it was contagious.

The program will be repeated tonight at 7 and tomorrow night at 8.