NEW YORK (AP) _ A study finding that one drug is better than a commonly used class of drugs at preventing deaths in people with high blood pressure may help change treatment recommendations in the United States, researchers say.

The study found that the drug metoprolol reduced the death rate by 48 percent in comparison to the widely used diuretics called thiazides, researchers said Thursday.

Metoprolol (pronounced muh-TAH-pro-lawl) is one of the heart drugs known as beta blockers. These drugs block the stimulating effect of adrenaline on the heart, reducing the rate and the force at which the heart pumps blood through the body - and reducing high blood pressure.

The thiazides make up one class of diuretics, which relieve high blood pressure by stimulating the body to expel fluid, thus lowering the total volume of blood in the bloodstream.

This is the first study to show that a beta blocker can prevent more deaths in people with hypertension than can thiazides, said the principal author of the study, Dr. John Wikstrand of Gothenburg University's Sahlgrenska University Hospital in Sweden.

It is therefore likely to require confirmation before being widely accepted, said Dr. Curt Furberg of the Bowman Gray School of Medicine in Winston-Salem, N.C., who was not associated with the study.

Two earlier studies that compared beta blockers and diuretics failed to find any significant difference in the death rate, he said in a telephone interview. The new study is interesting, he said, but ''I'm not sure how it's going to be accepted. It's possible we need to test it in a separate study.''

Wikstrand and colleagues at 66 centers in Europe and Canada monitored 3,234 men given either metoprolol or diuretics for a median period of 4.2 years. The researchers found a 48 percent lower death rate among men given metoprolol than those given diuretics.

The drop was mostly due to a reduction in deaths from stroke and coronary heart disease, two complications of high blood pressure, the researchers said. There was no significant effect on other causes of death, suggesting that the drugs are safe, they said.

The results of the study appear today in the Journal of the American Medical Association.

The American Heart Association estimates that 59 million Americans suffer from high blood pressure, or hypertension.

''We now have scientific proof that if we start with a beta blocker ... we will have a substantial reduction in deaths,'' Wikstrand said at a news conference at New York's Plaza Hotel.

The news conference was sponsored by metoprolol's developer, the Astra pharmaceutical company of Sweden, and by Ciba-Geigy Pharmaceuticals, which holds the license to market the drug in the United States, where it is sold under the trade name Lopressor.

Customary practice in the United States had been to prescribe diuretics first for high blood pressure and to try beta blockers later if the diuretics weren't working, said Dr. Stevo Julius of the University of Michigan Medical Center in Ann Arbor.

Julius, who was not part of the study, joined Wikstrand at a news conference at New York's Plaza Hotel to discuss the study's findings.

New recommendations by a committee of the National Heart, Lung and Blood Institute say that diuretics, beta blockers, or two newer classes of anti- hypertension drugs can serve as the first-line treatment for high blood pressure, said Julius, an adviser to that committee.

The Wikstrand study may increase the likelihood that doctors will choose beta blockers first, Julius said.