The medical community is having second thoughts about stents.

Tiny metal sleeves placed in arteries to keep blood flowing, stents have become such a popular quick fix for clogged coronary vessels that Americans will receive more than 1.5 million of them this year.

And stents are a big business, generating $6 billion a year in sales for their makers and thousands of dollars in fees for each procedure performed by the specialists implanting them.

But now stent sales are falling and some doctors are rethinking their faith in the devices, driven by emerging evidence that the newest and most common type — drug-coated stents — can sometimes cause potentially fatal blood clots months or even years after they are implanted.

The Food and Drug Administration said yesterday that it would hold hearings in early December to consider whether to issue new stent safety guidelines.

The evidence indicates that overuse of stents may be leading to thousands of heart attacks and deaths each year, whether because stents are being used in relatively mild cases where drugs should be prescribed instead, or because patients are receiving drug-coated versions where simpler, cheaper bare-metal devices might work just as well.

There is no question that stents have saved countless lives in the short term by preventing impending heart attacks or opening arteries while an attack is being treated. But neither type of stent, no matter how much better it may make a patient feel, has been shown in rigorous clinical trials to improve long-term survival compared with other forms of treatment.

“In the past we’d say, ‘Why not?,’ ” said Dr. William O’Neill, a well-known cardiologist at the University of Miami and longtime advocate of using drug-coated stents. But the new safety data, he said, amounts to “a big why not” for many patients.

The new evidence has added to a long-simmering debate over whether doctors have been too quick to prescribe stenting — whether because drugs would work as well for healthier patients or because bypass surgery might help the sickest ones live longer.

With the older bare-metal stents, the main drawback was the tendency of the repaired artery to become clogged again, in a process known as restenosis, that in severe cases led to repeated procedures or the trauma of more invasive bypass surgery. Drug-coated stents are credited with cutting the frequency of severe restenosis by about half.

But now the drug-coated versions are being shown to carry their own, potentially even more dangerous risks.

Stent makers and some doctors who use them argue that those risks are being overblown. New, less alarming interpretations of the clotting data are expected to be showcased next week at a conference in Washington of stent equipment makers and more than 10,000 doctors who do the procedures.

Those presentations will argue that even if delayed clotting is more common with the drug-coated stents than with metal stents or bypass surgery, the overall death and heart attacks rates are similar, according to spokesmen for the companies and conference organizers.

For those in the industry, the medical question has big financial implications.

The stenting specialists are typically not the physicians who would prescribe surgery or a drug regimen to heart patients. And so a downturn in the use of stents could have a direct impact on the specialists’ livelihoods.

But even some of the nation’s busiest stent centers, like Mt. Sinai Medical Center in New York, say the risk reports have made them more cautious.

“Six months ago, about 92 percent of the stents we used were drug-coated,” said Dr. Samin K. Sharma, the director of interventional cardiology at Mt. Sinai. “Now we are down to 85 percent.”

He cites the case of a patient, Jerry Ford, a 63-year-old Queens woman, who suffered a heart attack on Sept. 10. Last Monday she received three bare-metal stents from Dr. Sharma in a procedure that only a few months ago, he said, would have involved drug-coated devices.

Mrs. Ford said from home the next day that she was happy with the choice because it was clear that Dr. Sharma thought it the best option. “But my daughter and I are going on the Internet now to research more about it,” she said.