cientists report two major advances today in the concept of using embryonic cells to regenerate human tissues, results that are expected to sharpen the clash between advocates of biomedical research and opponents of abortion.

The advances come as the Bush administration, facing intense lobbying from the two sides, is reviewing the Clinton administration's proposal to let government-financed scientists proceed with the research.

In one of the reports, biologists at the National Institutes of Health used mouse embryonic stem cells to generate insulin-producing organs resembling the islets of the pancreas, a feat that holds promise for treating Type 1 diabetes, also known as juvenile diabetes.

In the other report, Rockefeller University biologists have proved in principle, though only in mice, the strange and once futuristic concept known as therapeutic cloning. The idea is to take an ordinary skin cell from a patient, convert it into an embryo and use the embryo's cells to repair any desired tissue of the patient's body. The embryo is destroyed in the process.

In this case the Rockefeller researchers chopped a tenth of an inch off the tails of mice and converted the tails' skin cells into embryonic stem cells. Colleagues at the Memorial Sloan-Kettering Cancer Center then made the stem cells morph into the dopamine-producing cells of the brain that are lost in Parkinson's disease.

Both studies are published in today's issue of Science.

The studies bolster hopes for a novel form of therapy referred to as regenerative medicine. Embryonic stem cells, taken from an embryo a few days old at the stage when it is a barely visible, hollow sphere of cells, are expected to play a central role in regenerative medicine since these powerful cells give rise to all the tissues of the adult body.

Probably as a defense against cancer, the body's adult cells are kept under tight leash and cannot divide very much or change into different types of cells. This constraint severely limits the aging body's ability to regenerate its organs and tissues, even though the information to do so still resides in every cell's genes.

But embryonic stem cells should be able to generate all medically desired new tissues, once biologists can find the right natural signals to coax them into any desired cell type. Though human embryonic stem cells were first obtained in 1998, almost all work on the cells is being done in mice, in part because federal financing for work on human embryonic cells has been in abeyance because of objections by abortion opponents, and in part because the mouse is a quicker and more practical test bed for working out the new principles.

Today's work with pancreatic cells, conducted by Nadya Lumelsky, Ron McKay and others in Dr. McKay's laboratory at the National Institutes of Health, lays the basis for a novel treatment of Type 1 diabetes, a disease in which the pancreas fails to produce insulin. The researchers devised a novel procedure for driving mouse embryonic stem cells down the particular line of development that leads to a pancreatic precursor cell. These precursor cells formed at least four types of pancreatic cells, including those that secrete insulin and two other hormones known as glucagon and somatostatin.

The different cell types then combined with each other in much the same architecture as do cells in the islets of the pancreas. This seems to be the first time that a miniature organ has been coaxed to form from embryonic stem cells, proof that in the right circumstances the body is a self-assembling system.

The islet-like structures produced insulin when exposed to glucose. When injected under the skin of diabetic mice, they induced the body to build a blood supply to them and enabled the mice to live longer. They did not produce enough insulin to cure the mice; Dr. McKay said more work was needed to mature the cells.

Last year Canadian researchers reported that transplants of human islet cells from donor organs had freed eight patients from the chore of daily insulin injections. There are not enough donor organs to treat the 16 million Americans who suffer from Type 1 diabetes. But if fully functional, islet-like structures could be generated from human embryonic stem cells, supply would not be a problem.

Dr. Lumelsky is trying to replicate the mouse work in human cells. Because researchers cannot use federal money to work on human embryonic stem cells, she has moved to the Harvard laboratory of Dr. Douglas A. Melton, who studies the cells with support from the Howard Hughes Medical Institute.

Dr. Melton said it was a burden, not a privilege, to be one of the few researchers able to work with human embryonic stem cells. "A result like Ron McKay's makes one see what kind of potential is going to be shut off by not funding this research," Dr. Melton said. "This is such an exciting area, not just for diabetes but for many other diseases, that rather than limiting the funds, one should aggressively pursue a line of research that holds such enormous promise."

Similiar frustration was expressed by Dr. Robert Goldstein, chief scientific officer of the Juvenile Diabetes Research Foundation. He said his organization was "very distressed," both that the large and expert corps of government-financed medical researchers were unable to work on the cells, and that the research now legally proceeding in the private sector lacked the benefit of public oversight. "Our magnificent biomedical research enterprise won't be working in this area, Dr. Goldstein said. "We think that is very unfortunate."

Abortion opponents object to the fact that embryonic stem cells are derived by destroying embryos and advocate using a different class of stem cell, known as adult stem cells, which are found in various adult tissues. But adult stem cells are less versatile; none can yet be converted into the tissues needed to treat diabetes and Parkinson's.

Today's other report proves that therapeutic cloning works in mice, although the researchers have yet to inject the dopamine-producing cells they created into the brains of mice with Parkinson's disease to see if symptoms are relieved. The creation of mouse embryonic stem cells from mouse skin cells was carried out by Dr. Teruhiko Wakayama and colleagues in the Rockefeller University laboratory of Dr. Peter Mombaerts. Dr. Lorenz Studer at Sloan-Kettering converted the embryonic cells into brain cells.

But to take therapeutic cloning from mice to people will not be simple. The mouse skin cell is converted to embryonic form by removing its nucleus and inserting it into a mouse egg whose own nucleus has been removed, the same process that was used in cloning Dolly the sheep. This egg is allowed to develop for a few days in glassware until it is a hollow sphere of some 120 cells. From these cells, which would form all the tissues of the mouse's body, embryonic cells are derived.

The same process in people might require a human egg cell to reprogram the skin cell nucleus. The embryo thus created could in principle be brought to term if inserted in a uterus, a procedure that would lead to cloning the person. Under therapeutic cloning, however, the embryo would instead be destroyed in order to create embryonic stem cells. Therapeutic cloning with human cells has been approved in Britain but in the United States it would not be permitted for researchers financed by the National Institutes of Health, even if the Bush administration were to let research with embryonic stem cells proceed.