ROME - Pope John Paul II sought Tuesday to lay down moral guidelines for medical research in the 21st century, endorsing organ donation and adult stem cell study but condemning human cloning and embryo experiments.
John Paul's address to an international conference of 5,000 transplant specialists appeared to be an attempt to set moral limits on such life-and-death issues as organ transplants and related research.
John Paul won applause from the transplant experts when he encouraged organ donation, calling it an ''act of love.''
But if his stance against embryo research were followed, ''all these people with serious diseases would have no hope,'' said one supporter of the research, Dr. Robert Goldstein of the New York-based Juvenile Diabetes Foundation.
Underscoring how important he considered the issue, the 80-year-old pontiff left his summer retreat at Castel Gandolfo outside Rome to address the International Congress of the Transplantation Society.
But the address went beyond being a booster speech for organ donations.
John Paul spelled out the church's position on transplant-related matters, condemning the sale of organs, insisting on informed consent on both sides of the exchange and singling out the complete end of brain activity as an acceptable way to determine that death has occurred.
Calling organ donation ''a genuine act of love,'' he said, ''Accordingly, any procedure which tends to commercialize human organs or to consider them as items of exchange or trade must be considered morally unacceptable.''
The decision on who should be first in line to receive organs can be based only on medical factors, John Paul said - not on age, sex, race, religion, social standing, usefulness to society or any other standard.
He left the door open for cross-species transplants.
The pope's support for organ donation was likely to have an impact on his 1 billion-strong flock of Roman Catholics. Traditionally, many Catholics have been adverse to both organ transplants and cremation for reasons having to do with keeping the body intact for resurrection.
John Paul also spoke out against cloning and related embryo research, a rapidly developing field in the four years since Dolly the lamb first struggled to its cloned hooves.
The pope renewed his opposition to both techniques just weeks after Britain moved toward allowing limited human cloning for research and the United States approving federal funding for research on human embryo stem cells.
The British and U.S. actions both grew out of scientific excitement about the promise of research on embryonic stem cells - parent cells that go on to form most types of cells and tissues.
Researchers hope the cells can some day be used to grow cells, tissues or whole organs - offering hope for scores of diseases from diabetes to Alzheimer's.
Experts say one of the most promising areas for the research is in Parkinson's - a neurological ailment of which the pope himself shows symptoms. The Vatican no longer denies he has it, although it has never confirmed it.
In the church's view, cloning is irreconcilable with its position that sex between married couples is the only acceptable way to create human life.
''Methods that fail to respect the dignity and value of the person must always be avoided,'' John Paul told the medical workers.
''I am thinking in particular of attempts at human cloning with a view to obtaining organs for transplants: These techniques, insofar as they involve the manipulation and destruction of human embryos, are not morally acceptable, even when their proposed goal is good in itself.''
John Paul ruled out use of embryonic cells as well, pointing scientists in the direction of adult stem cells as the acceptable route for research.
Adult stem cells already have been the object of research for up to 25 years now, with minimal results, said Goldstein, speaking by telephone from New York.
In all this time, ''there's no indication, none whatsoever, that adult stem cells have the same effect as embryonic,'' Goldstein said.
''For those people, where they have no other hope, this offers remarkable hope and promise,'' he said.
The British and U.S. moves have prompted the Italian government to consider a public referendum on whether Italy should follow their lead.
''All points of view merit appreciation and a calm and open discussion, without preconceptions or dogma,'' Italian Health Minister Umberto Veronesi said after the pontiff's speech.
One Italian scientist, Dr. Severino Antinori of Rome, says he needs only approval from a national bioethics committee - which includes religious representatives, including a Roman Catholic cardinal - to start working on a fertility treatment for humans.
In Italy, ''the religious groups are blocking it,'' Antinori said. ''That is very dangerous in the world.''