Neoadjuvant Radiation Therapy and Capecitabine in Treating Patients With Stage III or Stage IV Colorectal Adenocarcinoma

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed colorectal adenocarcinoma * Clinical stage T3, T4, N+ * Measurable disease * Awaiting surgery and likely to benefit from neoadjuvant radiotherapy PATIENT CHARACTERISTICS: Age * 18 to 80 Performance status * ECOG 0-2 OR * Karnofsky 60-100% Life expectancy * Not specified Hematopoietic * Absolute neutrophil count at least 2,000/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 10 g/dL Hepatic * Bilirubin no greater than 1.5 times upper limit of normal (ULN) * AST and ALT no greater than 2.5 times ULN * No hepatic condition that would interfere with study medication Renal * Creatinine clearance at least 80 mL/min * No renal condition that would interfere with study medication Cardiovascular * No serious cardiac failure with the past year * No myocardial infarction within the past year * No cardiac insufficiency * No angina * No uncontrolled arrhythmia * No uncontrolled hypertension Gastrointestinal * No superior intestinal tract malfunction * No malabsorption syndrome Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No concurrent serious infection * No other serious illness * No other malignancy within the past 5 years except curatively treated basal cell skin cancer or carcinoma in situ of the cervix * No metabolic condition that would interfere with study medication * No dementia or altered mental status * No psychiatric illness that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * No prior chemotherapy for colorectal cancer Endocrine therapy * Not specified Radiotherapy * No prior radiotherapy for colorectal cancer Surgery * Not specified Other * More than 30 days since prior participation in another clinical study