Easley Blackwood seems to be the Chicago Symphony Orchestra’s favorite local contemporary composer. In 1971 the CSO commissioned him to write his Fourth Symphony for its 80th anniversary. Now his Fifth Symphony is ready–this time for the CSO’s centennial. Over the years the longtime University of Chicago faculty member (and polymath)–who’s studied composition under Messiaen and Hindemith, conducting under Bernstein, and piano under Nadia Boulanger–has moved away from the radical tendencies of his youth; lately, for example, he’s rediscovered the virtues of tonality. With his latest symphony, he says, he tried to come up with a style that would have been Sibelius’s had he confronted modernism in 1915. (Sibelius, of course, was one of the last great symphonists; he stopped writing music partly because he was exhausted in his effort to carry classicism into the 20th century.) Also a purist, Blackwood intends his fifth to be “an expression of musical ideas, and nothing more.” The companion works on the CSO program are unabashedly romantic: Rachmaninoff’s Piano Concerto no. 1 (to be played by Garrick Ohlsson) and Schumann’s Symphony no. 2. James DePreist is the maestro. In an unusual move by the CSO, which normally repeats a program only twice, Blackwood’s symphony will be performed at six concerts (including two in June). Today, 1:30 PM, Saturday, 8 PM, and Tuesday, 7:30 PM, Orchestra Hall, 220 S. Michigan; 435-6666.