Scientists reported Sunday they had found a plentiful source of stem cells in amniotic fluid – the fluid that cushions babies in the womb – and produced a variety of tissue types from these cells, sidestepping the controversy over destroying embryos for research.

The stem cells – shed by the developing fetus and easy to harvest from the fluid leftover from amniocentesis tests given to pregnant women – were able to transform into new bone, heart muscle, blood vessels, fat, nerve and liver tissues, the study said.

The cells are easier to maintain in laboratory dishes than embryonic stem cells. The study also suggests another advantage: Unlike embryonic cells, which can form tumors when implanted in lab animals, amniotic fluid stem cells do not appear to do so.

“So far, we’ve been successful with every cell type we’ve attempted to produce from these stem cells,” said Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest University School of Medicine in Winston-Salem, N.C., and senior author of the report published online by the journal Nature Biotechnology.

Researchers at Wake Forest and Harvard University reported they were able to extract the stem cells without harm to mother or fetus.

“Our hope is that these cells will provide a valuable resource for tissue repair and for engineered organs as well,” Atala said.

Dr. Dario Fauza, coordinator of the surgical research laboratories at Children’s Hospital Boston, has used the cells to grow tissue to repair defective diaphragms and tracheas in sheep. He has asked the Food and Drug Administration for permission to do the same for children born with herniated diaphragms.

Two Swiss scientists have used amniotic fluid stem cells to grow heart valves and are testing them in sheep.

However, the scientists noted they still don’t know exactly how many different cell types can be made from the stem cells found in amniotic fluid. They also said that even preliminary tests in patients are years away.

“They can clearly generate a broad range of important cell types, but they may not do as many tricks as embryonic stem cells,” said Dr. Robert Lanza, a prominent embryonic stem cell researcher and head of scientific development at Advanced Cell Technology Inc. in Worcester, Mass.

The hallmark of human embryonic stem cells, which are created in the first days after conception, is the ability to turn into any of the more than 220 cell types that make up the human body. Researchers are hopeful they can train these primordial cells to repair damaged organs in need of healthy cells.

Atala and other scientists emphasized that they don’t believe the new cells will make embryonic stem cells irrelevant.

“There’s not going to be one shoe that fits all,” Lanza said. “We’re going to have to see which ones are most useful for which clinical conditions.”

George Daley, a Harvard stem cell researcher, echoed that sentiment. “They are not a replacement for embryonic stem cells,” he said.

The finding points to a promising avenue of research that sidesteps the hurdles facing embryonic stem cell research, which has been stymied by moral objections to the destruction of embryos that occurs when cells are harvested.

Last year, President Bush vetoed a bill that would have allowed federal funding of research on stem cells from embryos discarded by fertility clinics. The newly Democratic Congress has promised to send the same or a similar bill to Bush’s desk, with the House slated to vote on the matter this week.