More than half the hypertensive workers at three auto plants where special monitoring programs were provided had their blood pressure lowered to normal and kept it there, doctors said yesterday.

The most dramatic blood pressure control was achieved at a clinic that provided medical treatment for hypertension right in the factory, a study in the New England Journal of Medicine reported.

In a three-year study at four Ford plants in southeastern Michigan, University of Michigan researchers found that the most important element was to provide follow-up services that educated people about the condition and supported and encouraged efforts to control it.

After three years, blood pressure was considered normal in 56 to 62 percent of the workers treated at three clinics that offered screening and follow-up services. The fourth clinic, which only took blood pressure readings and referred the worker to a physician, reported blood pressure control in only 21 percent of the employes.

The Journal also reported that men who have had vasectomies run no greater risk of getting heart disease than men who have not been so sterilized, according to two studies of 6,300 medical records by the University of Oxford, England. In 1978, a Science magazine article reported that vasectomies increased the sev- erity of atherosclerosis--choles- terol deposits in the arteries--in monkeys.