Oxaliplatin, Leucovorin, and Fluorouracil Before and After Radiation Therapy and Surgery in Treating Patients With Rectal Cancer That Can Be Removed by Surgery

DISEASE CHARACTERISTICS: * Histopathologically confirmed rectal adenocarcinoma meeting the following criteria: * Inferior aspect of tumor is \> 4 cm from anal verge on digital examination and pelvic MRI scan * Superior aspect of tumor is not higher than the anterior aspect of the S1/S2 interspace on pelvic MRI scan * Mesorectal fascia is not threatened or involved (tumor \> 1 mm from mesorectal fascia) * Primary tumor meets 1 of the following criteria: * T3a-b (mesorectal primary tumor invasion seen ≤ 5 mm beyond muscularis propria) in the presence of 1 of the following: * Extra-mural vascular invasion * Mesorectal lymph node(s)/tumor deposit(s) with irregular border and mixed signal intensity * Any T3c (primary tumor invasion seen \> 5 mm beyond muscularis propria)-T4a (invasion of visceral peritoneum for tumors with a component above peritoneal reflection) * Low tumors should not involve levator ani (\> 1 mm gap between tumor and levator ani) or anal sphincters * No evidence of distant metastases or stage T4b cancer with invasion into adjacent organs or structures * Must have measurable disease at the baseline visit * Impending rectal obstruction is permitted if relieved by a non-functioning ileostomy or colostomy * No disease threatening mesorectal fascia (disease ≤ 1 mm from mesorectal fascia whether this is primary tumor, extra-mural vascular invasion, or tumor deposit with irregular border and mixed signal intensity) PATIENT CHARACTERISTICS: * ECOG performance status 0-1 * Hemoglobin ≥ 9 g/dL * WBC ≥ 3 x 10\^9/L * Absolute neutrophil count ≥ 1.5 x10\^9/L * Platelet count ≥ 100 x10\^9/L * Total bilirubin ≤ 1.5 times upper limit of normal (ULN) * Alkaline phosphatase ≤ 5 x ULN * AST or ALT ≤ 2.5 x ULN * Creatinine clearance ≥ 50 mL/min * Magnesium and calcium normal * Candidate for systemic therapy, in the opinion of the primary oncologist * No known significant impairment of intestinal absorption (e.g., chronic diarrhea, inflammatory bowel disease) * No evidence of established or acute ischemic heart disease (e.g., left bundle branch block, pathological q-waves, ST elevation, or ST-segment depression) and normal clinical cardiovascular assessment by ECG * No enlarged pelvic sidewall lymph nodes * No severe local bowel symptoms of tenesmus or irregularity or frequency of bowel habit precluding accurate assessment of diarrhea * No pelvic sepsis * No uncontrolled infection * Not pregnant or nursing * Fertile patients must use effective contraception during treatment and for 6 months after completion of treatment * No other prior or current malignant disease that, in the judgement of the treating investigator, is likely to interfere with study treatment or assessment of response * No clinically significant cardiovascular disease, including any of the following within the past year: * Myocardial infarction * Unstable angina * Symptomatic congestive heart failure * Serious uncontrolled cardiac arrhythmia * No history of interstitial lung disease (e.g., pneumonitis or pulmonary fibrosis or evidence of interstitial lung disease) PRIOR CONCURRENT THERAPY: * No prior pelvic radiotherapy * No metallic colon stent or rectal stent in situ * More than 30 days since prior chemotherapy, radiotherapy, hormonal treatment, antibody therapy, immunotherapy, gene therapy, vaccine therapy, angiogenesis inhibitors, matrix metalloproteinase inhibitors, thalidomide, anti-VEGF/Flk-1 monoclonal antibodies, or other experimental drugs