Classical Beethoven, Ludwig van: Symphony No. 9 in D minor for Piano, Chorus, and Orchestra, Op. 80 Emanuel Ax, piano. Margaret Price, soprano; Marilyn Home, mezzo-soprano; Jon Vickers, tenor; matti Salminen, bass. New York Choral Artists; New York Philharmonic, Zubin Mehta, conductor. (RCA Red Seal digital ARC2-4734) - These performances were recorded live in New York City on Feb. 2, 1983. Mehta always rises to gala occasions, and this was a very gala one indeed. A vocal quartet of unprecedented strength was assembled; ''Live From Lincoln Center'' was on hand to broadcast the event live on PBS; and RCA was making a permanent aural document of the concert. It has the presence of a live event, and the flaws. Mehta's reading of the Ninth Symphony may not be one for the ages in the Furtwangler sense, but it is a handsome one nonetheless, full of life, vigor, power. The singing is not as good as it might be - Mr. Vickers and Miss Price were both in less-than-ideal voice. For my tastes, the reason to own this two-record set is the performance of the ''Choral'' Fantasy. Emanuel Ax's performance of the elaborate piano part is superb. This fine young artist is coming boldly into his own, and here he makes the very most of a wonderful opportunity. The sound throughout is fine.