 This randomized phase III trial is studying eflornithine and sulindac to see how well they work compared to a placebo in preventing colorectal cancer in patients with colon polyps. Chemoprevention is the use of certain drugs to keep cancer from forming, growing, or coming back. The use of eflornithine and sulindac may prevent colorectal cancer. It is not yet known whether eflornithine and sulindac are more effective than a placebo in preventing colorectal cancer 