Drivers with diabetes or epilepsy may face a one-third-higher risk of auto accidents than other people, probably because of the chance that they will black out and lose control of their cars, according to a study published last week in the New England Journal of Medicine.

Despite their findings, however, researchers said they do not believe further restrictions should be placed on the driving privileges of people with these common diseases.

All states require people with epilepsy to stay off the road for periods ranging from three months to two years after their last seizure. In most states, diabetic drivers also need letters from their doctors assuring that they are not prone to blackouts.

"There is a slight increase in risk for both epileptics and diabetics, but the increase is small enough that we didn't feel there was any great need to change current driving restrictions," said Phiroze Hansotia of the Marshfield Clinic in Wisconsin, who directed the study.

However, in an editorial published with the study, Julian A. Waller of the University of Vermont questioned this interpretation, especially for people with more severe forms of the diseases.

"The author's conclusion that there is little to worry about may be absolutely correct for some persons with these diseases but premature for others," he wrote.

An estimated 14 million Americans have diabetes, and 2.5 million have epilepsy.

The study was based on a review of all car accidents and driving violations among 30,420 people who lived within 25 miles of the clinic in rural Wisconsin. Among them were 484 people who have diabetes and 241 with epilepsy.

Virtually everyone in the Marshfield area is treated at the clinic, so the researchers believed they could identify nearly all residents with those diseases.

They found that epileptics had a 33 percent higher accident risk and diabetics a 32 percent higher risk than the rest of the population. Both groups also were more likely to be stopped by the police for careless driving.

The researchers maintained that the increased risk of accidents associated with epilepsy and diabetes is small compared to some other factors. Of the 5,665 accidents in the Marshfield area during four years of study, 13 were attributed to epileptic seizures. By comparison, drivers under age 25 had 1,058 more accidents than would have been expected if they had the same accident rate as older drivers.

The study did not determine precisely why the diabetics and epileptics had more accidents. However, Hansotia said their diseases were likely to have contributed.

"Both the epileptic and diabetic patients are at risk for traffic accidents because they lose control over their body movements or lose consciousness," he said. "In the epileptic patient, it occurs because of seizures or convulsions. In the diabetic patients, it is because of a hypoglycemic episode."

Diabetics who must take insulin injections are at risk of low blood sugar levels, or hypoglycemia.

Richard Kahn of the American Diabetes Association said diabetics should be evaluated individually to see whether they can safely drive. "There are people with diabetes who should not be drivers," he said. "But the overwhelming majority could be drivers and be as safe as people without diabetes."