Lincoln Center's Mostly Mozart Festival opened last night at the Kennedy Center, a week before its opening at its customary New York stand, and it drew an almost soldout house.The report is that tonight's concert will be completely S.R.O.

From the first moments of the pre-concert recital, it was clear that the highest kind of music-making was in store. Close to two-thirds of the concert hall was filled for the curtain-raiser in which pianist Emanuel Ax and cellist Yo-Yo-Ma played the second of Beethoven's five sonatas for cello and piano.

Their performance was an augury of things to come, since they were also the soloists in the orchestral program that began an hour later. The sonata is Beethoven in his purest, pre-turbulent idiom, gleaming with inspired melodies ideally treated on both instruments. Ma's handling of the pianissimo flying arpeggios in the finale were the stuff of dreams, as was all that Ax did with the piano, not the least of which was his ideal dynamic balancing.

Leonard Slatkin conducted the festival orchestra in the concert that followed, providing a mounting array of discipline and dazzle that reached a peak of excitement in the final of the Symphony No. 36 in C, the "Linz." He opened with a solid account of the overture to "Cosi fan tutte," before providing Ax with elegant orchestral support for the Concerto in B Flat, K. 456.

As is often the case in the last dozen or more of Mozart's concertos, it is impossible, while listening to this one, to think of anything more ravishing or more a matter of sheer inspiration in melodic invention, in instrumental textures -- especially in the woodwinds -- and in harmonic imagination. Ax played with the utmost perception, couching all that he did in pianism of unusual glory.

For Ma's concerto, the music turned from Mozart to the Haydn of 1783, the Concerto in D. Glorying in the splendid new bow he has had for only a few weeks, Ma delighted in feathery sounds in rapid passages, frequently displaying a pianissimo of faultless control and shading, while giving the songful episodes a golden sheen.

The audience, which was vociferous in its applause for soloist and conductor all evening, called Ma back after the Hayden until most of the house had risen to its feet. Tonight Alicia de Larrocha is the soloist with Slatkin and the orchestra.