Ex-Chicagoan Ned Rorem returns to Orchestra Hall–where he got the informal portion of his musical education more than half a century ago–with an ambitious, brand-new vocal work, one of the Chicago Symphony’s nine centennial commissions. Entitled Goodbye My Fancy, the hour-long oratorio is vaguely autobiographical, with texts based on the prose and poetry of Walt Whitman, for whom Rorem has a special affinity. The work’s 19 movements are grouped into three large sections, loosely chronicling the life of a dedicated artist: “Now Voyager” (set to Withman’s early verse), sensual and carnal, is about self-discovery; “The Strayed Dead” looks unflinchingly at the tragedy of the Civil War (based on the pained and candid observations in Whitman’s diary); and the music in “The Harvest According” settles into the conetmplative comfort and wisdom of old age. As underrated now as he was overcelebrated in the 50s and 60s, Rorem is a musical conservative with a theatrical turn of mind, but he’s also indisputably one of the great exponents of the art song. This rare all-American CSO outing, under the baton of Leonard Slatkin, also includes Walter Piston’s Symphony no. 2 (1948) and John Corigliano’s Three Hallucinations (from his Oscar-nominated score for Ken Russell’s 1981 film Altered States). The soloists in the Rorem oratorio are mezzo Wendy White and bass John Cheek. (An all-day seminar on American music and American composers, with talks by Rorem, Corigliano, and CSO’s new composer-in-residence Shulamit Ran and including chamber music performed by CSO players, will begin at 9 today in the Orchestra Hall ballroom.) Tonight and Saturday, 8 PM, Orchestra Hall, 220 S. Michigan, 435-6666 or 435-8122.