More than 600 patients with severe heart pain who took a single aspirin daily for 12 weeks suffered far fewer heart attacks than patients who didn't take aspirin, a group of doctors said yesterday.

Research teams at 12 Veterans Administration hospitals gave the equivalent of an aspirin a day to 625 men with "unstable angina": new or worsened chest pain caused by dangerously reduced blood flow to the heart.

In the three months of treatment--a period of great risk of an outright, often fatal heart attack--these men had just under half as many heart attacks as a group not given aspirin.

Half as many of the aspirin-treated men died, though the number of deaths, in contrast to the number of heart attacks, was too small to be statistically significant.

The doctors' report in today's New England Journal of Medicine is certain to heighten interest in common aspirin as a possible preventive measure for cardiovascular disease, that is, both strokes and heart attacks. Aspirin tends to prevent the formation of chemicals that make blood platelets clump and choke off blood flow, which, in turn, helps cause heart pain and attacks.

Previous studies have shown that aspirin can help prevent strokes in persons who suffer transient ischemia--temporary losses of blood flow to the brain. Efforts to demonstrate that aspirin would have a similar effect in preventing a second heart attack have been less certain.

But, in the latter case, the aspirin treatment was started well after the attacks had occurred, past the period of initial danger, Dr. H. Daniel Lewis, chief of cardiology at the Kansas City Medical Center and chairman of the 12-hospital group, said in an interview.

Also, he said, the aspirin was given more frequently and in larger doses in the earlier studies. Where a single aspirin may inhibit blood clumping, a larger dose may irretrievably trigger chemicals that keep blood vessels from expanding. This may cancel the aspirin's hoped-for effect of helping to keep blood and fresh, life-giving oxygen flowing to the heart.

The upshot, said Dr. James Davis, chief of hematology at the Kansas City hospital, is that "you probably need to give not only smaller doses of aspirin, but also give it less frequently, such as once a day, as we did."

Aspirin is also being used in efforts to prevent strokes and heart attacks in the healthy. A Harvard University study now under way involves giving aspirin to 10,000 doctors each day for four years, plus carotene to try to prevent cancer.

But, Lewis warned, "we can't say" yet that taking aspirin to prevent cardiovascular disease is "appropriate" for men or women in general. Aspirin can also trigger stomach or intestinal bleeding, and the long-range effects of its use in the healthy are still unknown.

Of the 625 patients given aspirin for 12 weeks, 31--about 5 percent--suffered acute, sometimes fatal heart attacks in that period, compared with 65, about 10 percent, in the no-aspirin group. Ten died, compared with 21 of the no-aspirin men. Follow-up was maintained for one year on 86 percent of each group. Even after a year, though no more aspirin was given, the death rate remained 43 percent lower in the aspirin group than in the no-aspirin group.

Like most such studies, the VA study was conducted only in men, who suffer premature heart attacks far more often than women. But one recent study did find aspirin equally effective in women in helping to prevent strokes, the VA doctors reported.