Researchers reported Friday they have the first evidence directly linking smoking and heart disease, but tobacco industry officials rejected the claim, saying the illness can be tied to a number of causes.

The study's authors say smokers were three times more likely than non-smokers to have angina, or chest pains, and painless periods of inadequate blood flow to the heart.An editorial accompanying the research in the Journal of the American Medical Association said the study was the long-sought "smoking gun" showing a link between smoking and heart ailments.

Gary Miller, a spokesman for the tobacco industry's Washington-based Tobacco Institute, disputed that, saying, "This is not enough evidence to make such a claim."

Miller noted the study involved only two dozen smokers. Forty-one non-smokers also participated.

The study, based at Brigham and Women's Hospital in Boston, was conducted by attaching a monitor to patients' hearts. The patients, all of whom had been diagnosed as having heart disease, wore the monitors for 24 hours while they went about their daily routines.

In tests from October 1984 to December 1987, the monitors showed 975 ischemic episodes, or periods of inadequate blood flow, 8 percent of which were accompanied by chest pains. The median number of episodes over 24 hours was three for smokers, one for non-smokers.

Dr. Andrew Selwyn, a co-author of the report and a Harvard Medical School associate professor, said ischemic episodes damage the heart temporarily and can lead to heart attacks.

But the short-term effects are "reversible and very treatable," the cardiologist said. "That's what makes it useful to show (the study) to patients and say `Look, you haven't damaged your heart yet, so stop smoking now,' " he said.

"This is a solid piece of evidence you can show patients before they actually have a heart attack," Selwyn said. "I hope it's ammunition that doctors use to show patients as often as possible."

The Tobacco Institute spokesman, however, said "anything can cause these ischemic episodes. Caffeine, excitement can cause them."

The study showed that the episodes lasted longer among smokers, whose median episode lasted 24 minutes compared with 2 minutes for non-smokers.

Both frequency and duration increased as the number of cigarettes increased, the study said.

"The more they smoke in general, the more ischemia they have and the greater their risk of heart attack and death," Selwyn said.

The accompanying editorial said research on smoking and heart disease until now has been based on indirect evidence.

What had been lacking was direct evidence, a "smoking gun" linking the two, wrote Dr. Peter F. Cohn of the Health Sciences Center of the State University of New York at Stony Brook.