Rachmaninoff, Sergei: ''Rhapsody on a Theme of Paganini.'' Saint-Saens, Camille: Piano Concerto No. 2 in G minor. Bella Davidovich, pianist. Concertgebouw Orchestra, Amsterdam, Neeme Jarvi, conductor. (Philips Digital 6514 164) The Rachmaninoff receives a gracious, suave performance here, with Miss Davidovich at home in all aspects of the demanding score, but especially deft at sustaining long melodies. Conductor Jarvi does a splendid job clarifying all the orchestral textures. But it is the Saint-Saens that makes this disc special. Nowadays, the tendency is to play this work as if it were written by Tchaikovsky. Here, it is treated like the elegant and flashy score Saint-Saens wrote, and that is cause for celebration. Miss Davidovich's gracious presence suffuses every page, and she does not shirk her virtuoso's responsibilities. Jarvi is the attentive conductor throughout. However, the sound is slightly muffled (a distressing surprise), and the piano at times almost vanishes in the Rachmaninoff. But it is, nonetheless, a fine sample of Miss Davidovich in the concerto context.