The Juilliard Dance Ensemble's production of ''L'Apres-Midi d'un Faune'' (''Afternoon of a Faun'') on Saturday night at the Juilliard Theater was a reminder of how comparatively few choreographic works have been notated over the centuries. Instead, dances are usually taught by one generation of performers to the next. Because memories play tricks, such a method of preservation can blur or distort a piece's nuances.

What made Juilliard's ''Faune'' special was the fact that, unlike most revivals of Vaslav Nijinsky's ballet of 1912, which are based on dancers' recollections, this one derived from a score of the work made in 1915 by Nijinsky himself in an idiosyncratic notation system that was long considered incomprehensible. But in 1987 it was deciphered by Ann Hutchinson Guest, an authority on notation who is married to the British dance historian Ivor Guest, and Claudia Jeschke, a West German dance historian and notator. The Juilliard production, staged by Jill Beck of the school's dance faculty and directed by Mrs. Guest, proved an eye-opener.

The ballet still depicted a shy faun's amorous encounter with some nymphs. And Leon Bakst's original scenery and costume designs were reproduced by John Brady and Thomas Augustine. What looked different was the quality of the movement.

Nijinsky was inspired by ancient Greek friezes and vase paintings, and his ballet abounds with sharp gestures, which, in recent revivals based on memory, are often allowed to become extremely angular. Because the accompanying score by Debussy is lush, some critics have even called ''Faune'' an early example of a ballet in which, instead of co-existing in harmony, music and choreography are experimentally juxtaposed. That statement cannot be made about the Juilliard staging.

Sharp angles still exist. But there are also many softer, gentler, more flowing phrases. If the choreography no longer appears determinedly unconventional, it now seems more varied than before, and when sharp gestures do come they have the effect of kinetic punctuation marks.

Only dance historians can determine whether this version is truly definitive, and questions can be asked about it. Do the notation symbols accurately convey Nijinsky's intentions? Did he unwittingly make mistakes in transcribing steps to paper? Did the reconstructors accidentally misinterpret any symbols? And how can the reconstructors know that the score is a record of the choreography of 1912 and not a blueprint for a future revision?

Whatever the answers to these questions may be, the Juilliard production looked convincing, and it was devotedly danced. Yoav Kaddar was a languid faun who delighted in playing the flute in the opening scene. Because of his stage presence and sense of timing, he held the attention in his meeting with the nymphs, who were led by Rebecca Stenn. At times, no one moved much. Nevertheless, every step took on importance and pauses were as significant as movements.

The program also included contemporary pieces, two of which made especially good impressions. After hurtling on stage, the dancers in Doug Varone's ''In Middle Ground'' slogged along, toppled over and picked one another up to an austere score by Christopher Hyams-Hart. The drab costumes by Mr. Augustine made it possible to wonder if these people were refugees. They were certainly struggling to survive. There were moments when a sameness of musical and choreographic texture threatened to make the work monotonous. Yet, for the most part, ''In Middle Ground'' managed to build dramatic tension without the aid of a specific plot.

Despite the adjective in its title, Monica Levy's ''Delicate Revolution'' was a blustery dance to the first movement of Stravinsky's Symphony in Three Movements. People kept tugging at one another and splitting apart, and solo figures barged their way through clusters of dancers. Although phrases were often fragmented, the work never shattered into bits, for the choreographer always managed to let the action sweep along.

Just as the suite by Respighi to which it was set combined Renaissance melodies with modern harmonies, so Gerri Houlihan's ''Ancient Airs and Dances'' was a contemporary commentary on courtly dances. It was a neatly made piece, although one without much emotional impact.

Genia Melikova's ''Interlude'' began impressively when Chenault Spence's lighting designs revealed the dancers posed in striking silhouettes. What followed was a murky drama to the first movement of Franck's Quintet in F minor for Piano and Strings. The plot ostensibly concerned an unhappy marriage. But dramatic situations became nothing more than pretexts for displays of classical steps, and the performance suggested that Juilliard students are more adept at contemporary than classical styles.

Fine accompaniment was provided by the Juilliard Orchestra, conducted by Bruno Ferrandis.