The death Wednesday night of artificial-heart recipient Jack C. Burcham occurred after a "jelly-like" blood clot squeezed a remaining portion of his natural heart, to which the device was attached, and cut off blood flow, doctors said today.

Surgeon William C. DeVries said Burcham's death, 10 days after doctors replaced most of his failing heart with a plastic-and-metal pump, will not halt such experiments at Louisville's Humana Heart Institute International.

Today, reaction to Burcham's death generally was muted, as many scientists took a "wait-and-see" attitude until DeVries completes his first seven artificial-heart implants and publishes his findings.

However, Arthur Caplan, a medical ethics expert with New York's Hastings Center, said the experience to date "makes it clear the device is still relatively primitive and we are in the first stage of human use . . . . It seems to me that Humana, by manipulating the press, built up expectations concerning therapy that are simply unrealistic, and recent events bear this out."

Dr. Claude Lenfant, director of the National Heart, Lung and Blood Institute said, "It has established one more time that the whole thing is still very experimental . . . . It's still too early to make a judgment . . . . I'm still personally extremely cautious about the future of heart replacement with a mechanical heart."

Dr. Allan M. Lansing, chairman of Humana Heart Institute International, said an autopsy did not reveal the cause of Burcham's internal bleeding that led to the jelly-like blood clot. But Lansing said that oozing of excess blood in the cavity between the heart and the lungs was probably related to Burcham's deteriorating kidneys and the use of drugs to thin his blood and prevent clots in the artificial heart. No clots were found within the artificial heart, he said.

DeVries, who has permission from the Food and Drug Administration to implant the Jarvik-7 artificial heart in seven patients, has completed four implants. A fifth Jarvik-7 implant, in Sweden, is not counted among that seven.

The Louisville artificial-heart implants are being funded by Humana Inc., a for-profit hospital chain whose officers have pledged to pay for up to 100 implants as long as progress is being made.

At 62, Burcham, a retired railroad engineer from LeRoy, Ill., was the oldest artificial-heart recipient, but survived the shortest time with an implant.

The first recipient, Seattle dentist Barney B. Clark, also suffered, like Burcham, from multiple complications but lived 112 days with the device before dying March 23, 1983.

Three artificial-heart recipients survive. William J. Schroeder, 53, today entered his sixth month of life with an artificial heart. He lives in a Louisville apartment across the street from Humana Hospital Audubon.

Murray P. Haydon, 58, has remained hospitalized since his Feb. 17 implant. He frequently is on a respirator but is improving steadily, Humana officials say.

Today DeVries emphasized the trial-and-error nature of the artificial-heart program, saying that each of his patients "will make a contribution" toward a better life for future implant recipients. "There's no question that we can take care of patients now better, after four patients, than we could after one, than we could after two or three."

But he acknowledged that Burcham's life may have been shortened by the experiment. Before the April 14 implant, Lansing said that although Burcham was suffering more severe kidney damage than previous recipients, he might survive two months without the operation -- the longest estimate for any of DeVries' four patients.

Burcham's surgery was expected to be smoother than his predecessors'. But problems began almost as soon as Burcham's original surgery was under way. Because doctors had overestimated the size of Burcham's chest, DeVries had to whittle part of the breast bone and twist the Jarvik 7's chambers slightly to make the device fit. The extra tugging on the sutures is thought to have contributed to bleeding that sent Burcham back for a second operation 24 hours after the implant and required that he be given 42 pints of blood.

DeVries said the tight fit probably had little to do with the formation of the blood clot that killed Burcham.

Throughout his life with the device, Burcham was bedridden and intermittently alert. But doctors had little warning of the compression of the remaining parts of Burcham's natural heart, a condition known as cardiac tamponade. Chest X-rays taken Wednesday morning appeared clear, and until about an hour before his death at 9:48 p.m., Burcham appeared in stable condition, Lansing said.

During dialysis that afternoon, a nurse noticed that Burcham's breathing was abnormal. Burcham was removed from dialysis, and a new chest X-ray showed blood accumulating near his heart. Lansing described the bleeding as "a diffuse ooze from the entire operative area." The jelly-like clot compressed the left atrium, squeezing blood back into Burcham's lungs.