If all's well that ends well, an excellent performance of Beethoven's Ninth Symphony was presented to an overflow audience Saturday night at Wolf Trap. This excellence, however, was a last-minute development, and primary credit goes not to the National Symphony, which was the orchestra for the occasion, but to the University of Maryland Chorus, which came to the orchestra's rescue.

The chorus -- one of the best -- celebrated its 20th anniversary and its 36th Beethoven Ninth by singing the final movement as well as I have ever heard it sung, live or on records. The soloists were good, particularly bass-baritone James Courtney and tenor Richard Leech, who had the most demanding assignments. Soprano Elizabeth Knighton and mezzo Cynthia Rose harmonized effectively. But Saturday night neither the soloists nor the orchestra seemed to be in the same league with the chorus.

The NSO was under the able baton of Hugh Wolff, who always knows exactly what he wants, usually manages to get it from this orchestra and has performed the Ninth triumphantly at Wolf Trap in the past. But this time, the orchestra's performance began raggedly, improved only slowly and never reached the level of precision shown by the chorus in the final movement. The chorus sounded, and undoubtedly was, much better-rehearsed than the orchestra.

The playing had considerable vitality, and there were some magnificent moments -- the timpani throughout; the cellos and double basses in the recitative passages that open the last movement. But the NSO as a whole often had problems getting together, at the level we expect of a major symphony orchestra, particularly in the first movement.

The reason is not difficult to find. This was the third program the orchestra had played at Wolf Trap in three days, and there simply was not time for adequate rehearsal of all three. Beethoven's Ninth may be totally familiar to each member of the orchestra, but when more than 100 musicians are going to perform together, they need a certain amount of time to coordinate, no matter how well they know the music. A lot of the ensemble adjustment that should have been done in rehearsal was done instead during the first movement.

The audience filled the Filene Center to capacity, and some occupied grassy spots outside, where the music could be heard clearly and no tickets were needed. It was a good-natured crowd that applauded after the first and second movements. But the long standing ovation after the last was more appropriate.