DISEASE CHARACTERISTICS: Histologically confirmed pelvic cancer Planned therapy is to undergo continuous definitive or adjuvant external beam pelvic radiation therapy with or without fluorouracil (5-FU) plus or minus levamisole No split course radiation therapy Planned course of radiation therapy must also meet the following criteria: - Entire pelvis must be encompassed by the planned radiotherapy fields - Total planned dose to the central axis midplane or isocenter for the whole pelvic field must be between 4500-5350 cGy - Treatment must be given 4-5 times per week on a one-treatment-per-day basis No stool incontinence or stool frequency of 7 or more per day prior to initiation of radiation therapy Must be entered on study before the second radiation therapy fraction No current or prior metastases beyond pelvic regional lymph nodes Must have functioning rectum No planned perineal irradiation No anal cancer No active intraluminal gastrointestinal (GI) tumors Patients with completely resectioned GI tumors who also receive adjuvant treatment are eligible

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Creatinine less than 2 times upper limit of normal Other: No known allergy to glutamine No history of inflammatory bowel disease No other medical condition that may interfere with treatment Not pregnant or nursing Adequate contraception is required of all fertile patients

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No concurrent leucovorin or other chemotherapy agents, except 5-FU with or without levamisole Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics No prior pelvic radiotherapy No brachytherapy prior to completion of all external beam radiotherapy Surgery: No abdominal-perineal resection, Hartmann procedure, or other surgical procedure that has left patient without a functioning rectum