ATLANTA (AP) _ A tiny diamond cutting tool spinning at 200,000 times per minute successfully tunnelled through deposits clogging arteries in 95 percent of 315 patients tested, scientists reported Monday.

''It has been an exceedingly useful device to treat blood vessels in a different way,'' said Dr. Maurice Buchbinder, a cardiologist at the University of California, San Diego.

Side effects were minimal, Buchbinder said in a report at the annual meeting of the American College of Cardiology. About 6 percent of the patients suffered heart attacks after the procedure, but most of those attacks were not the most severe type, he said.

There were no deaths and about two-thirds of the patients' arteries remained open six months after the procedure, he said.

Dr. William Untereker of the Philadelphia Heart Institute, an authority on the use of lasers to open blocked arteries, said it is too soon to know how the diamond-tipped device will compare with lasers or other devices intended to scour the inside of arteries.

''A lot of this is theoretical,'' he said. ''We think with the laser we're getting a clean cut. I would predict it would be a year or two before this is sorted out,'' he said.

He reported a 96 percent success rate using a laser to open re-clogged blood vessels in patients who had previously undergone bypass surgery.

Buchbinder's device, called a Rotablator, is manufactured by Heart Technology Inc. of Bellevue, Wash. It was developed by David Auth, the company's chairman.

The Rotablator is powered by compressed air that runs a turbine outside the body, turning a flexible shaft threaded through the artery. The egg-shaped tip, covered with thousands of microscopic diamond chips, cuts hard materials such as the tough plaques that clog arteries but does not cut flexible tissue, such as the artery walls, Buchbinder said.

''It's very similar to the way a razor spares your skin while cutting the stubbles with the rotation,'' he said.

Dr. Michel Bertrand of the University of Lille, who is collaborating ith Buchbinder on studies of the device, reported that unclogged arteries closed abruptly in 4.5 percent of the patients treated. But in all cases the arteries were reopened, usually with an inflatable balloon threaded into the artery, he said.

Bertrand and Buchbinder are compiling data on patients being tested at 15 research hospitals in the United States and Europe, Buchbinder said.

In about one-third of the patients, an inflatable balloon was used to further open arteries after the diamond tip cut away most of the blockage, Buchbinder said.

The cutting tool will not replace the balloon, which is used routinely to open clogged arteries, he said.

But, ''for lesions that are higher risk with the balloon, this may have particular advantages,'' he said.

Unlike the balloon, the Rotablator does not put stress on the artery walls, he said.

And when a balloon is used after the Rotablator, doctors can use much less pressure to squeeze remaining plaque against the sides of the artery, because the Rotablator has softened the plaque, Buchbinder said.