For their spring series at the Library of Congress, the Juilliard is playing nine of the 16 Beethoven string quartets, the rest to be featured at their concerts here in the fall.

Last night they directed their talents, energy and concentration on his first quartet, Opus 18, No. 1, the surpassingly beautiful quartet in A Minor, Opus 132, and the middle period quartet, Opus 59, No. 3. The ensemble was in unusually well-knit form, and all three works sounded newly considered and rethought.

The third movement of the A Minor quartet contains some of the most remarkable sonorities in all of music. Its hymn-like phrases, with widely spaced voices and unusual doubling, requires the most sensitive control and balance, and the Juilliard treated it with powerful intensity touched with just the needed degree of gentleness. It was a memorable performance.

The focus of the Opus 18 quartet was on the Adagio movement, where the Juilliard chose to highlight Beethoven's emerging stylistic vocabulary while allowing the expressive and passionate aspects of the music to declare themselves with no particular help. This was a good decision. There is so much of interest in the purely musical aspects of this movement that a lot of emoting can only get in the way.

The concluding quartet, Opus 59, No. 3, moved with refreshing directness and comparative simplicity until the last movement, which violist Samuel Rhodes started off at an incredible speed. His three collaborators kept up the pace, and there is no doubt that the result was exciting. The excitement, however, was achieved at the expense of clarity, ensemble and common sense.

The concert will be repeated tonight and broadcast over WETA-FM. It shouldn't be missed.