S0304 Induct Chemo Then Chemo-RT in Pts w/Locally Advanced Adenocarcinoma of the Rectum

RATIONALE: Drugs used in chemotherapy, such as irinotecan, leucovorin, fluorouracil, and oxaliplatin, use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining radiation therapy with chemotherapy may kill more tumor cells. PURPOSE: This phase II trial is studying how well different regimens of induction chemotherapy followed by chemoradiotherapy work in treating patients with locally advanced adenocarcinoma of the rectum.