Eating fresh fruit and green vegetables may help prevent strokes, two British scientists say in the current issue of Britain's leading medical journal.

What's more, say Profs. Roy Acheson and D.R.R. Williams of Cambridge University, the fact that people have been eating more fruits and vegetables may be one reason this deadly disease has declined remarkably in nations such as the United States and Britain.

Strokes--blockages or breakdown of brain arteries--still strike 500,000 Americans a year and kill 170,000.

But the incidence of strokes has been on a sharp decline for at least 30 years in Great Britain and the United States.

Between 1970 and 1980 alone the U.S. death rate declined by nearly 40 percent.

In England and Wales it declined by 15 to 20 percent between 1950 and 1974.

In the current issue of the Lancet, the Cambridge epidemiologists ask why, and conclude: "Eating fresh fruit and fresh green vegetables does indeed seem to be associated with reduced risk of early death" from strokes.

Their suggestion comes less than a year after a National Academy of Sciences committee said Americans could help prevent cancer by eating more fruits, vegetables and whole-grain bread and cereals, as well as less fatty, salted or smoked meat, butter, whole milk and alcohol.

The British scientists say there are probably many reasons for the reduction in strokes.

One recent reason, many authorities believe, is better control of high blood pressure, which often can lead to a stroke.

Also, salt intake has been on the decline since the advent of refrigeration in industrialized countries. Excess consumption of salt can trigger high blood pressure in many people.

Strokes are also often associated with heart disease. Both may be associated with high-fat, high-cholesterol diets that clog blood vessels.

The Cambridge scientists examined stroke statistics--and fruit and vegetable consumption, among other possibilities--in different areas of Britain and different economic classes.

They found a striking correlation among income, residence in low-stroke areas and fruit and vegetable consumption.

In general, the higher the economic class, the greater the consumption of fruits and vegetables.

The Britons label their idea a "hypothesis" and take account of some conflicting evidence, but say in summation that fruits and vegetables "may offer a safe and agreeable form of preventive medicine."

It is possible, they add, that the protective element in fruits and green vegetables may be vitamin C.

The academy committee likewise urged increased vitamin C consumption--from fruits and vegetables rather than pills.

A Lancet editorial called the Acheson-William hypothesis "potentially very important" but requiring more study.

At the National Institutes of Health here, Dr. Artemis Simopoulos, nutrition coordinator, said it "makes some sense."

"Studies have shown that about half of all patients with essential unexplained hypertension are salt-sensitive," she said.

"In general, when you eat more fruits and vegetables, you automatically lessen your sodium intake.

"Fruits and vegetables have very little sodium. So if people eat more of them, as they have been doing, fewer should get hypertension and strokes."