There's new confusion in the heartland. Medical historians have long noted that once somebody finds a cure or treatment for one disease, another crops up like a new bulge in a well-worn carpet. This time it's a Lulu and it has to do with that most controversial of substances: cholesterol. No sooner have we gotten a grip on cholesterol's effect on heart disease than we find ourselves wrestling with its role in causing cancer.

Once it seemed simple, at least to cardiologists of the persuasion of the American Heart Association.Eat less high-cholesterol and saturated-fatty foods. Try to get your blood cholesterol as low as possible. The rock-bottom number of 150 milligrams of blood cholesterol has been called "ideal" by some heart experts, and 180 milligrams the "desirable norm."

Now some new findings are putting the brakes on that philosophy. The long-term studies on people who have conscientiously reduced their blood cholesterol are coming in. And there's a curious anomaly. In some cases the men (not women) who had the lowest serum cholesterol didn't get as much heart disease. But they died just as soon, and were more likely to develop cancer, most noticeably colon cancer.

Hints of a low cholesterol-cancer connection showed up in studies as long as 10 years ago. But they weren't taken seriously until a cluster of new studies in 1980 showed the same thing. The one that rocked scientists the most is the famous Framingham heart study. It showed to the "surprise and chagrin" of government heart experts that those with the lowest cholesterol died at younger ages. For example, men with cholesterol below 190 milligrams had three times as much colon cancer as those with higher cholesterol. A couple of other studies sponsored by the National Heart, Lung and Blood Institute also showed cancer-low cholesterol associations. In a Honolulu study, incidences of stomach, colon, liver and lung cancers increased as cholesterol levels sank. In a Puerto Rican study, stomach and esophageal cancers increased.

These quirky results -- hardly what anybody anticipated -- have sent the architects of low-cholesterol diets back to the drawing boards, and have resulted in frequent comment in medical journals. An editorial in the May 22/29 Journal of the American Medical Association reviewed the link between low cholesterol and cancer and concluded: "(The findings) reinforce doubts that we yet know enough about the consequences of lowering the serum cholesterol level to consider its reduction in the general population by either drug or dietary means."

At a recent meeting at the National Institutes of Health, experts tried to sort out what it all means. Dr. Robert Levy, director of the Heart Institute, says, "It probably means we have to stop thinking that the lower the blood cholesterol, the healthier it is for us. We at the institute have never recommended trying to reduce your cholesterol below 200. And I still think that's the best advice."

Evidence presented at the meeting showed that about 5 to 10 percent of American men with low cholesterol -- under 180 milligrams -- do have a higher risk of cancer. And the group of experts agreed that such men should be warned against eating a low-fat diet to reduce their cholesterol further. Women, it appears, don't have to worry. Nobody knows why.

The experts are going round and round in their discussion of possible explanations. Some theories: The cancer may cause the low cholesterol -- instead of the other way around. Or the cholesterol may be a "marker" -- a statistical corollary indicating a predisposition to cancer -- and could be used diagnostically to spot potential cancer victims. Or low-fat intakes could lead to a vitamin A deficiency, predisposing one to cancer. It's all vague right now. Dr. Levy says it will be years before the reason for the cancer-cholesterol connection is clear.

In the meantime, some doctors are concerned that the new evidence will smash their well-orchestrated efforts to get the population off high-cholesterol foods. Most agree these foods are associated both with heart disease -- and wouldn't you know it -- cancer. So what's a person to do? While our modern medicine men study the ever-changing kaleidoscope of knowledge, it seems best to fall back on the wisdom of the ancients: moderation. Translated, Dr. Levy says that means: If your blood cholesterol is much more than 200, try to get it down. A cholesterol level of 250 quadruples your chances of heart disease. Otherwise, if your cholesterol is 200 or below, forget it. And if your cholesterol is way under 200 -- by 20 or 30 milligrams -- should you try to raise it by eating fatty foods? No. Doctors don't know nearly enough to recommend that. It could be risky and unnecessary.

So if you've been fighting to reduce your cholesterol to sub-basement levels, you can relax. No use saving yourself from heart disease, only to fall into an early grave from cancer. But, alas, most of us, in this land where the average cholesterol level for adults runs over 220, can't stop trying. Experts say that through diet we can reduce our cholesterol by at most 10 to 15 percent -- not enough to plunge us into the cancer danger zone, but maybe enough to save us from heart disease.