Amid signs of some outside acceptance of his controversial experiment, Dr. Leonard L. Bailey said today that a blood-type difference may have doomed the first baboon-to-baby heart transplant but that the problem could be solved within a year.

Bailey's comments came in the current edition of the Journal of the American Medical Association, in a news conference today and a three-hour briefing Wednesday for print reporters. The same issue of JAMA carried an editorial arguing that even if the blood had matched, tissue incompatibility would have proved fatal.

In his first detailed scientific report on the procedure, Bailey defended his work at the Loma Linda University Medical Center as a "reasonable investigative option" and said he was still unsure why month-old Baby Fae died in November 1984 after 20 days with the heart of a year-old baboon.

Medical experts say Bailey's work has alerted physicians and parents to the country's critical need for infant heart transplants and may have slightly reduced the shortage of human donors that led Bailey to experiment with baboons.

Bailey said that if laboratory tests confirm that a blood-type difference killed Baby Fae, he can obtain baboons with the proper blood in at least half of the cases and "provide the potential for those babies surviving indefinitely."

The guest editorial challenged the claim of Bailey and Loma Linda immunologist Sandra L. Nehlsen-Cannarella that they had found a way to match baboon and human tissue.

But the authors, Dr. Olga Jonasson of the University of Illinois and Dr. Mark A. Hardy of Columbia, concluded that Bailey has demonstrated that a heart transplant from another species is technically feasible in an infant, and that rejection of the foreign heart can be largely suppressed by the drug cyclosporine, and that the procedure "might serve as a most suitable short-term support" for an infant with fatal heart defects "until a human heart donor can be found."

Arthur L. Caplan, a New York medical ethicist who had questioned the operation last year, concluded in another JAMA article that such experiments were "ethically defensible . . . where no reasonable alternative therapy exists." Doctors here said Caplan appeared to have a change of heart after visiting the facility and talking to Baby Fae's mother, who again endorsed the experiment in a statement released today.

Caplan said in an interview that his earlier criticism had been "hypothetical" and said he still feels that such experiments should require federal approval.

Baby Fae, like approximately 500 other American babies each year, was born with hypoplastic left heart syndrome, a severe deformity that usually results in death within a month if untreated.

Bailey said he thought outside experts were becoming more receptive to baboon-to-human experiments as efforts to repair such hearts continue to have only mixed success. A two-stage repair procedure developed by Dr. William Norwood of Philadelphia Children's Hospital has been completed successfully in three patients, and at least half of babies with the heart defect appear unsuitable for the procedure or are unable to survive the first stage. Bailey said he has tried unsuccessfully to repair, rather than replace, such hearts three times in the last year.

Although Bailey's experiment has increased interest in possible human donors, they remain extremely rare. Last Nov. 20, Bailey successfully performed a human-to-human transplant on a four-day-old infant known as Baby Moses, but Bailey said finding the donor heart was the result of "layers and layers of serendipity."

A videotape of Baby Moses, who has survived longer than any other infant after such an operation, today showed a healthy-looking, dark-haired boy in yellow pajamas yawning and grasping a nurse's finger.

Bailey said that several parents have asked him to try to save their babies with baboon heart transplants but that he has resolved to delay a second operation until his investigation of the Baby Fae experiment is complete. One father in Washington state "literally begged me to let them come down here," Bailey said. He put them in touch with Norwood, but the infant died before a trip to Philadelphia could be arranged. He said the incident left him feeling "awful."

Bailey said the autopsy on Baby Fae indicated that a clumping of red blood cells resulting from the blood-type difference may have starved the heart for blood and also injured the kidneys, liver and lungs. He also speculated on the possible harmful effects of antibodies attacking the foreign heart tissue and of the cyclosporine used to depress the baby's immune system so she would not reject the animal heart.

Bailey said that with Baby Fae near death and a decision imperative, Bailey's laboratory staff had completed all tests on possible baboon donors except the blood-type test. Bailey said it was a "reasonable risk" to go ahead with the operation anyway because other cross-species transplants had achieved some success without a blood match and because it was highly unlikely they could find a donor with O-type blood, extremely rare in baboons, to match Baby Fae.

Bailey hopes to seek university permission for a baboon-to-human transplant operation in 1986 and said he may have to reject infants who have O-type blood while hoping that selective breeding eventually can produce some usable O-type baboons.

He added that he will also seek a human donor before performing any new baboon transplant, a failure in the Baby Fae case that produced criticism from editorial writers and federal officials. He said he would also curtail use of a nutrient rich in fat that may have absorbed toxic concentrations of cyclosporine in Baby Fae.

In their editorial, Jonasson and Hardy rejected Bailey and Nehlsen-Cannarella's contention that tests had shown Baby Fae's tissue was compatible with the baboon. They said that using human typing reagents to type baboon tissues was "essentially irrelevant" because of the vast difference in species.

Nehlsen-Cannarella, the immunologist, suggested today that the two critics had misread her work. She said she was not attempting to type the baboon tissue, only to see if they had some compatible reactions to Baby Fae's. She said that the two doctors were citing an out-of-date 1972 report to back up their critique.

Bailey challenged the contention that baboons would not be suitable donors because of their distance from humans on the evolutionary tract. He acknowledged that chimpanzees, which do not reproduce well in captivity, might be better donors but argued that it was best to test all potential primate donors in laboratory animal-to-human tissue culture experiments to see which would work.