To watch Awadagin Pratt at the keyboard is to witness contradiction in motion. Built like a halfback, the 26-year-old pianist is capable of both tremendous volume and the tenderest of touches. He hunches over the piano with the oblivious abandon of Stevie Wonder, but he's a classical performer to the core--a Naumburg prizewinner with diplomas in piano, violin, and conducting from the Peabody Conservatory. About the only reservation I have about this rising star--who grew up in Normal, where his father taught school--is his predilection for large-scale popular showpieces where he can dazzle rather than enlighten; there's a danger he may end up another Van Cliburn, forever stuck in the groove of a flashy, limited repertoire. At this Chicago Sinfonietta concert the Grieg Concerto will offer ample opportunity for Pratt to display awesome physical power. Maestro Paul Freeman will also guide the well-regarded multiethnic ensemble through the local premiere of George Butterworth's A Shropshire Lad and Shostakovich's First Symphony. The lyrical, neoromantic tone poem by Butterworth, an Oxford-educated ethnomusicologist who died young in battle in 1915, was inspired by the poetry of A.E. Housman. The Shostakovich is also a youthful work: in its emotional intensity and sardonic wit we can't help but notice the early promise of one of our century's great symphonists. Sunday, 2:30 PM, Rosary College, 7900 W. Division, River Forest. Monday, 7:30 PM, Orchestra Hall, 220 S. Michigan. 857-1062.