Kelly Ryan Leeper, his round face framed by long chestnut hair, giggled and fidgeted in his father's arms, looking as fat, alert and rosy-cheeked as any baby born in this booming Los Angeles suburb.

Yet six months ago Kelly was near death, born with the same severe heart defect that led doctors at Loma Linda University Medical Center 30 miles away to implant a baboon's heart in another endangered newborn, Baby Fae.

Baby Fae is dead, her transplanted animal heart fatally weakened by her body's natural defenses and by kidney failure. Kelly Leeper is very much alive, transformed by surgical wizardry in Boston into a robust infant with a cheery demeanor that makes him, in his mother's words, "the best baby you ever saw."

From the minute it was revealed that the parents of Baby Fae had elected to try a baboon transplant rather than corrective surgery, medical ethicists and editorial writers questioned their decision and criticized the Loma Linda doctors who discussed it with them.

The story of Kelly Leeper reveals no simple failure of judgment on the part of Baby Fae's parents and doctors, however, but a host of problems -- low birth weight, parental shock and uncertainty, long distances and insurance -- that suggest that anyone who succeeds in saving these infants by any method is performing a miracle amid great risks.

When Stephanie Leeper, 28, a gymnastics instructor, and Charles (Chas) Leeper, 31, a Realtor and lay minister, brought their third child, Kelly, home from the hospital May 23, he appeared to be a healthy -- if somewhat quiet -- baby, weighing 6 pounds, 6 ounces. Their older children, Faith Ann, 7, and Chas Jr., 5, had been born at least six weeks premature. They were glad that drugs and bed rest had allowed this baby to wait almost to full term.

After the next day's rush of events -- Kelly's troubling failure to nurse, a mad dash between three hospitals, the final diagnosis of hypoplastic left heart syndrome -- the Leepers learned how important those weeks had been in producing a baby strong enough to withstand the rigors of the operation ahead.

Kelly had Baby Fae's problem, a heart whose left side was almost missing, leaving him dependent on tubes of food and oxygen snaking into nearly every part of his body. Hypoplastic left heart syndrome occurs in more than 300 babies a year in the United States; it accounts for 25 percent of all cardiac deaths in the first week of life.

With the hindsight of a man whose son was saved by the Boston operation, Chas Leeper asked of Baby Fae, "Why did they put a baboon heart in instead of doing this?"

But as the Leepers learned from the beginning, Kelly had no more than a 40-percent chance of survival with the heart-repair technique practiced in Boston and Philadelphia, and that was only the first part of a two-stage process that only two children have completed successfully.

Kelly, born before the animal-to-human heart transplant was even an alternative, also had several advantages. He was more than a pound heavier than Baby Fae. His parents learned about the Boston procedure within two days of his birth and were far more willing to consider a long trip for a risky procedure than were Baby Fae's young, unmarried and relatively inexperienced parents.

In his first public comment on his discussions with Baby Fae's parents about the Boston procedure, Dr. Leonard L. Bailey said through a Loma Linda University hospital spokesman this week that he offered the parents help in arranging for transportation of the baby to Boston. "They never gave it any consideration," Bailey was quoted as saying.

The point of the baboon transplant, Bailey has said from the start, is to see if a ready supply of hearts from easily acquired animals can give threatened babies a quick new lease on a full life, rather than leaving them with a still-deformed heart whose circulation has been cleverly rerouted but not restored to normal by doctors in Boston or Philadelphia.

Transplanting hearts from other infants remains a poor third choice; there are not enough such hearts available and there rarely is enough time to prepare them for use in such critically ill babies.

When doctors ushered Kelly Leeper's parents into a stark conference room at Children's Hospital of Orange County and informed them of their son's condition, both were shocked. The baby had only a small chance of survival with the East Coast operation, and probably would not last the night anyway. Brain or kidney damage was likely.

Stephanie Leeper's first reaction was "to go ahead and let him die." The suffering he faced seemed unbearable. On the way home late that night, their car broke down just off the highway. While they walked to call help, they began talking about their feelings.

Back home with friends, Chas found an unexpected optimism creeping over him. Like his wife, he was a born-again Christian and he found hope in a verse from the 73rd Psalm: "My flesh and my heart faileth: but God is the strength of my heart, and my portion for ever."

That attitude was crucial to what happened the next day, when the Leepers returned to the hospital to find that Kelly unexpectedly had survived the night. A special drug, prostaglandin, had managed to keep open a duct that usually closes after birth and dooms such babies to long sleep ending in quiet death.

The Leepers and their doctors had to decide what to do. In a situation in which every option holds the chance of suffering and death, doctors try to "get a feeling for what the parents have to say" before making any recommendations, said Dr. Paul Pitlick, a Stanford University pediatric cardiologist.

Doctors at Stanford have tried the East Coast operation, sometimes called the Norwood procedure after Dr. William Norwood of Philadelphia, but have failed to make it work. Discussing the options with the parents of such babies, Pitlick said, "is a very difficult thing to deal with."

But at the Orange County hospital the next morning, Chas Leeper was determined to try the operation. The doctors suggested that they first check for brain damage, but he insisted that that did not matter. The Leeper's insurance, a nurse told them, did not cover the operation, but she had become caught up in the Leepers' determination and suggested a plan.

According to Chas Leeper, the nurse offered to call in local television and newspaper reporters and ask for public contributions. Then she called the Leepers' insurers to let them know that the news media was interested in the story.

A spokesman for Blue Cross of California said the decision to cover the operation was last-minute and frantic, but there was no indication of an initial decision against the Leepers. Such unusual requests are decided "on a case-by-case basis," the spokesman said.

Dr. Aldo Castaneda, the cardiac surgical chief who worked with Norwood in developing the procedure at Boston Children's Hospital, said he knows of no major insurers who have declined to cover the operation.

The Leepers' insurance paid not only the $39,000 hospital costs and $4,000 surgeon's fee, but the $17,000 cost of a chartered jet to take Kelly and Chas Leeper to Boston. An oxygen pump gave out in midflight; a nurse pumped oxygen manually for the baby the last hour.

The most important factor in determining the success of the surgical procedure, Castaneda said, is operating as soon as possible after birth.

Martha Bare, whose 3-month-old baby, Keith Lawrence Bare, is doing well after the operation, said her child was rushed from her maternity ward in Mount Holly, N.J., to Philadelphia Children's Hospital within hours of his birth. It was so quick she could not leave to be with her baby as Norwood, now chief of cardiac surgery at the Philadelphia hospital, performed the operation.

Kelly Leeper flew to Boston on a Saturday. The operation, the 83rd of its kind, was performed Sunday morning. Norwood and Castaneda were out of the country, but Boston surgeon Richard Jonas performed the operation, with assistance from cardiologist Peter Lang.

Stephanie Leeper, who later joined her husband, paled at the sight of Lang's long hair and drooping mustache.

"He looked like a hippy . . . like he'd just come back from smoking dope," she said. "The first thing I said to myself was, 'I'm not going to let you touch my baby.' "

But Lang soon won them over, and brought them encouraging reports of how Kelly's strength and high birth weight had increased his chances. Kelly sailed through the four-hour operation, and was sent home after two weeks, whereas the average stay had been three months. All medication was discontinued after three months.

During their short stay in Boston, the Leepers saw the unhappy side of the experiment. Another baby died after the same operation.

"That was the hardest," Stephanie Leeper said. "We had gotten to know the parents."

Now nearly 14 pounds, Kelly Leeper faces another crisis. His body eventually will outgrow the synthetic shunts attached to his heart. Sometime between his first and fourth birthdays, he will need a second operation to reroute his circulation again. The second operation, Norwood said, is designed to allow for a fairly normal adult life, although the patient will tire much more quickly during strenuous exercise than someone with a normal heart.

The oldest surviving subject of the Norwood procedure is 4-year-old Julie Pritchett of Anchorage, Alaska.

According to Julie's father, Mike, a 33-year-old salesman, Norwood failed in August to complete the second phase in the repair of Julie's heart. Her lungs, he said, had not developed sufficiently and several more months must pass before doctors can try again.

Julie was late in talking and her speech still is slightly slurred, which her mother, Paula, feels is a vestige of her heart ailment. Two other children, younger than Julie, have successfully completed the second Norwood operation, while another has died as a result, the Pritchetts said.

After her unsuccessful August operation, Julie fought off pneumonia and a virus associated with blood transfusions. But the Leepers, the Bares and other parents whose children have been saved from almost certain death after birth rarely think about the dangers ahead.

Chas and Stephanie Leeper still treasure the memory of Kelly's triumphant appearance at their church after their return from Boston, a Thanksgiving Day come early for friends who had held their hands, raised money and prayed for the baby.

"He's loved by so many and he's touched so many lives," Stephanie Leeper wrote in her diary. "We give the glory to God. We enjoy every minute we have with Kelly."