CONCERT AUDIENCES had more staying power in the old days -- or perhaps they demanded more for their money than we do today.

Take, for example, the concert of April 12, 1800 in Vienna's Burgtheater, when Beethoven's First Symphony was unveiled to the world. Besides this substantial premiere, the program included Beethoven's First Piano Concerto, his Septet in E-flat, a Mozart symphony and selections from Haydn's oratorio "The Creation" -- at least a concert and a half by modern standards. To fill out the time and give the patrons their money's worth, the sponsors of the concert also promised that "Herr Ludwig van Beethoven will improvise on the pianoforte."

This Friday night in the Departmental Auditorium, the Smithsonian Resident Associates will sponsor a replay of that program, slimmed down for the modern audience. The Mozart and Haydn selections and the improvisation will be omitted. Otherwise, this concert will be as much as possible like the original occasion.

The orchestra is the Hanover Band of London, an organization of specialists who play Beethoven on old instruments tuned to the original pitch (somewhat lower than the modern A440 cycles per second) without the services of a conductor. Those who wonder how Beethoven's music must have sounded when it was new should find the concert a fascinating experience.

As heard on an English import record (Nimbus 2151, 2 LPs), the Hanover Band is somewhat less extreme in its dynamics than modern orchestras, which are more than three times as large. In Beethoven's Fifth Symphony and his Third Piano Concerto, the sound is gentler, less brilliant and biting than a modern orchestra, the phrasing nimble but more relaxed. Those who like lots of tension in their Beethoven will get more of it from Solti or Bernstein or any of the dozens of others who have interpreted this music on records.

But this interpetation -- based on the consensus of professional musicians -- removes a sort of filter between Beethoven and the listener. It also preserves all the drama and excitement that the composer originally put on the page, and that is plenty.

HANOVER BAND OF LONDON -- On record with Beethoven's Fifth Symphony and Third Piano Concerto (Nimbus 2151); in concert, with pianist Melvyn Tan performing on a 1798 Broadwood piano, performing Beethoven: Symphony No. 1, Piano Concerto No. 1, Septet in E-flat. Friday at 7 p.m. at the Departmental Auditorium, on Constitution Avenue between 12th and 14th streets NW. For information, 357-3030.