NEW ORLEANS — People with low cholesterol and no big risk for heart disease had dramatically lower rates of heart attacks, death and stroke if they took the cholesterol pill Crestor, a large study found.

The results, reported Sunday at an American Heart Association conference, were hailed as a watershed event in heart disease prevention. Doctors said the study might lead as many as 7 million more Americans to consider taking cholesterol-lowering statin drugs, sold as Crestor, Lipitor, Zocor or in generic form.

"This takes prevention to a whole new level, because it applies to patients who we now wouldn't have any evidence to treat," said Dr. W. Douglas Weaver, a Detroit cardiologist and president of the American College of Cardiology.

The study also gives the best evidence yet for using a new test to identify people who may need treatment, according to a statement from Dr. Elizabeth Nabel, director of the National Heart, Lung and Blood Institute. The new research will be considered by experts reviewing current guidelines.

However, some doctors urged caution. Crestor gave clear benefit in the study, but so few heart attacks and deaths occurred among these low-risk people that treating everyone like them in the United States could cost up to $9 billion a year — "a difficult sell," one expert said.

About 120 people would have to take Crestor for two years to prevent a single heart attack, stroke or death, said Stanford University cardiologist Dr. Mark Hlatky.