Sometimes the Mostly Mozart Festival's typical formula for a concert--back-to-back soloists on each side of the intermission--can be too much of a muchness. The evening may be too long. One virtuoso may overshadow another.

But when the players are of the caliber of pianist Emanuel Ax and violinist Nadja Salerno-Sonnenberg, who played with the Mostly Mozart Orchestra last night at the Kennedy Center, the complainer about so much muchness is left empty-handed.

Ax's caressing way with the 17th piano concerto, K. 453, was bewitching. Not even in "The Magic Flute" does Mozart's euphoric mode glow more unblinkingly than in this concerto. Ax captures the almost conversational character of this concerto's poetry just about as fetchingly as one could imagine. The tone was unfailingly beautiful. Rhythms were exactly precise, in an inconspicuous way. The music never failed to breathe. Dynamics were marvelous (especially in the first digression from the main theme in the last movement). The work was embraced in warmth without ever seeming sentimental.

This quality of Mozart playing is something the new generation of American Mozart pianists has brought to us that we did not have before. With earlier generations, American playing was sometimes too muscular for Mozart's delicate nuances (with the notable exception of Eugene Istomin). But today the Mozart playing of Ax--and of his contemporaries Murray Perahia and Peter Serkin--is peerless. In the 17th, the Mostly Mozart Orchestra, under Gerard Schwarz, sounded stylish.

The less experienced Salerno-Sonnenberg did not phrase at quite this level, but she wasn't far behind. Her version of the Third Violin Concerto was classically proportioned and eminently thoughtful. The profoundly soulful slow movement was not yet as passionate, though, as it is in the hands of Isaac Stern, for instance.

Salerno-Sonnenberg's technique was formidable indeed. From top to bottom the tone was rich and even. Her command of the notes was flawless. At only 22, she appears to be a major talent.

She and Ax had never played together before this week, but in what the Mostly Mozart Festival calls its "pre-concerts"--chamber music recitals that come an hour before the main concert--the two were elegant Mozart stylists in the Mozart violin and piano sonata K. 304.

Ax also played the Brahms A Minor and A Major intermezzos, Op. 118. His performance of the lyric A Major, especially, was enchanting.

Schwarz also led the orchestra in energetic, if not exactly electrifying, versions of the J.C. Bach Sinfonia in D and the Mendelssohn "Italian" Symphony.