OBJECTIVES: I. Assess the local recurrence rate, cost-benefit ratio, and acute and late toxicity associated with concomitant preoperative radiotherapy and fluorouracil/leucovorin (5-FU/CF) in patients with locally advanced adenocarcinoma of the rectum. II. Compare the relapse rate, survival rate, disease-free interval, and cost-benefit ratio associated with 6 courses of postoperative 5-FU/CF vs. no further treatment in these patients.