Radiation Therapy Plus Chemotherapy Before Surgery With or Without Chemotherapy After Surgery in Treating Patients With Rectal Cancer

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining more than one drug, giving the drugs in different ways, and combining chemotherapy with radiation therapy may kill more tumor cells.
PURPOSE: Randomized phase III trial to compare the effectiveness of radiation therapy plus fluorouracil and leucovorin before surgery given with or without fluorouracil and leucovorin after surgery in patients with locally advanced rectal cancer.