OBJECTIVES: I. Compare the overall and relapse free survival of patients with stage II or III rectal cancer treated with one of the following three regimens: bolus injections of fluorouracil (5-FU) prior to and following pelvic irradiation plus protracted venous infusion (PVI) 5-FU radiosensitization vs PVI 5-FU prior to and following pelvic irradiation plus PVI 5-FU radiosensitization vs bolus 5-FU with leucovorin calcium and levamisole prior to and following pelvic irradiation. II. Describe relapse patterns and tolerance associated with these regimens in these patients.