Shortly after 8:30 last night, Sarah Caldwell walked out on the big stage at Wolf Trap, raised her baton, and began conducting the National Symphony Orchestra in what were unmistakably the opening measures of the Ninth Symphony by Beethoven. Never mind that the program said, "Consecration of the House," Overture. What Caldwell was conducting and what the musicians were playing was the Ninth Symphony. The overture was dropped without announcement of any kind.

The symphony, however, was what the thousands who had disregarded unfriendly thunder and downpours shortly before the concert had come to hear. Even the wet grass did not discourage a large number of law sitters. And when the symphony was, over, the ovation was long and thunderous.

There was good reason for the enthusiasm. Boston's preeminent conductor of both opera and symphony had a solid grasp of the large and challenging work. From the opening notes, her conception unfolded in logical ways. The first movement was not the intense driving matter it is with other conductors. It was, perhaps, more Bruno Walter than Toscanini. However, it can be noted that Caldwell brought the entire symphony in at about one minute over Toscanini's usual time of 65 minutes. After an opening movement that was at times appropriately lyrical, she moved into the scherzo with an unyielding drive that created genuine excitement. The orchestra's fine playing throughout this movement was one of the chief factors in the mounting tension.

The slow movement was a long song, beautifically delineated by the strings, with lovely playing in the woodwind choir. Taking its ritards deliberately and dividing the beat for the finest effect, Caldwell made clear the sustained singing line Beethoven threaded through it.

For her vocal colleagues in the finale, Caldwell had the superb University of Maryland Chorus, trained by Paul Traver, well known for its uniform excellence in the Ninth. The solo quartet was unusually musicianly, with soprano Phyllis Bryn-Julson, contralto Eunice Alberts, tenor Dennis Bailey and bass James Morris projecting both words and notes with a kind of accuracy and musicality that is rarely so evenly encountered. Bryn-Julson, for the remarkable handling of the flying top notes and her exquisite final soft phrase, and Morris for the solid richness of his opening recitative, deserve special praise. So does Bailey for his excellent enunciation and phrasing of the most difficult of the solo passages.

Caldwell held the assorted moods of the movement together with the kind of direction that comes from long knowledge of its purpose. The final pages were a proper whirlwind.