Fluorouracil and Leucovorin and/or Levamisole After Surgery In Treating Patients With Dukes' B Or Dukes' C Colon Cancer

RATIONALE: Drugs used in chemotherapy, such as fluorouracil, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Leucovorin may help fluorouracil kill more tumor cells. Biological therapies, such as levamisole, may interfere with the growth of tumor cells and slow the growth of solid tumors. It is not yet known whether fluorouracil is more effective when given together with leucovorin and/or levamisole after surgery in treating colon cancer. PURPOSE: This randomized phase III trial is studying giving fluorouracil together with leucovorin to see how well it works compared with giving fluorouracil together with levamisole, or giving fluorouracil together with leucovorin and levamisole after surgery in treating patients with Dukes' B or Dukes' C colon cancer.