Murray P. Haydon, who is to undergo surgery to become the world's third recipient of an artificial heart here Sunday at 8 a.m., has a much better prognosis than either of the previous recipients, said Dr. Allan M. Lansing, director of Humana Heart Institute International.

"We feel he will be a much more adequate test of the artificial heart and its function than anyone else before," Lansing told reporters.

Haydon's heart disease is slightly less advanced than that of the previous recipients. Barney B. Clark was rushed into emergency surgery for his artificial-heart implant, and William J. Schroeder probably would have died within hours had he not received an artificial heart. Haydon could be expected to live another two or three weeks but would be bedridden and withering, Lansing said.

"He understands that he is failing steadily. And he also understands that the farther down the line you are, the harder it is to recover and get back. So he would rather take the leap now than wait until he is on his last gasp," Lansing added.

The only area in which Haydon is less well off is nutrition. He has lost 25 pounds in the last three weeks and, according to Lansing, looks thin, tired and gray.

Haydon, 58, is "the ideal candidate" for the experimental operation, with none of the complications suffered by the two previous artificial-heart recipients, said Dr. Jerome Lacy, the cardiologist who has treated Haydon for four years.

Haydon suffers cardiomyopathy of unknown origin, a debilitating disease of the heart muscle. His weakening heart has grown oversized. Schroeder's heart was in the same condition before his implant, but his cardiomyopathy was known to be the result of narrowed coronary arteries.

Doctors suspect that arterial disease lead to Schoeder's stroke. They consider Haydon less likely to have a stroke because he does not have that condition. To further prevent a stroke, Haydon is to receive anticoagulants several days earlier than Schroeder did.

Haydon first showed signs of heart disease in 1981, when he began to feel weak and short of breath at his job as a production worker at a Ford Motor Co. auto plant in Louisville. His illness forced him to leave his job several months later and become sedentary.

He had done "fairly well until the past two months," taking drugs that stimulated his heart and dilated his blood vessels to decrease resistence to blood flow, Lacy said. Then, in early January, "he started going downhill fast."

Haydon checked into another Louisville hospital about two weeks ago for treatment with the drug amrinone, which strengthens the heart muscle and makes it beat faster. His heart responded well to the treatment, but its activity declined after the drug was stopped.

At one point last week, Haydon's heart was failing so badly that Lacy told Haydon's family that he might die within hours. But after several family discussions Haydon decided to explore the possibility of an artificial heart. "In a way, it was a surprise for him" to consider an artificial heart, because his decline was so sudden, Lacy said.

Lacy told Haydon that "if he lived in any other city I would probably only be able to hold his hand and offer moral support. But . . . here, we have this alternative."

DeVries has said artificial-heart candidates must live within an hour's drive of the hospital so they can receive essential family and community support.

Most of Haydon's recent weight loss has been muscle tissue that is starved for blood. In contrast to Schroeder, who could barely lift his head from the pillow before the implant, Haydon can take a few steps at a time, but such exertion leaves him breathless and exhausted.

Haydon was admitted to Humana Hospital Audubon Wednesday and cleared Thursday by the six-member patient-selection committee.

"He's very keyed-in to the possibility that he could have a stroke, but he's not thinking of the complications," Lacy said. "He's thinking of getting out and going home. He just really wants to live.

"He was in World War II, was in combat zones. He's a real survivor."

Haydon's relatives and friends describe him as quiet, optimistic and devoted to his family. He and his wife of 32 years, Juanita, have three adult children. Their fifth grandchild was born yesterday to the wife of his son Derek. The baby, delivered at Audubon, was named Daniel Murray Haydon.

Haydon's former supervisor, Bob Ecker, recalls the day in October 1981 when he realized the extent of Haydon's heart trouble. "We were just having a talk, and he told me he felt bad and wanted to go to First Aid. I said go on and go, and he never came back after that."