Radiation Therapy, Surgery, and Chemotherapy in Treating Patients With Rectal Cancer That Can Be Surgically Removed

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 radiation therapy and surgery with chemotherapy may kill more tumor cells. PURPOSE: Randomized phase III trial to compare radiation therapy alone before surgery with radiation therapy plus fluorouracil and leucovorin before surgery, with and without fluorouracil and leucovorin after surgery in patients with rectal cancer that can be surgically removed.