The Chicago Symphony Orchestra, which stunned the orchestra world when it posted an unprecedented $6 million deficit last year, has officially balanced its books for the 2002-03 season. The CSO cut $2.5 million from its annual budget and took an additional endowment draw of $1.3 million in order to stay out of the red, while ticket sales and contributed income remained flat. However, the orchestra anticipates a return to large deficits for the current season, when it will not be able to repeat the endowment overdraw trick.