Brain disorders may be corrected in the unborn using stem cells, scientist say in a study. The report comes as President Bush weighs federal policy on funding embryonic stem cell research.

An experiment with monkeys offers the promise of allowing damaged brains to be repaired during gestation, according to the study in the journal Science. The researchers say that human neural stem cells injected into the skulls of three unborn monkeys became an integral part of the developing brains of the animals.

The study means it may be possible to use stem cells to repair a damaged brain before a child is born, said Dr. Curt R. Freed, a researcher at the University of Colorado School of Medicine.

"The clinical implications are potentially profound," said Freed, a co-author of the study. "This suggests we could repair the developing human brain in utero and have a child born normally that would otherwise have a defect that could lead to failure of the brain in the first few years of life."

Freed and Dr. Evan Y. Snyder of Harvard Medical School led a team of researchers who developed a way to treat Parkinson's disease in adults by injecting into their brains fetal neural cells that make dopamine, a brain chemical that is deficit in Parkinson's.

Although the researchers used stem cells from an aborted fetus, Freed said further research may show that repairing the brain could best be done using neural stem cells that are grown from embryonic stem cells.

Embryonic stem cells are extracted from a human embryo. Researchers have shown those stem cells can be directed to transform into other types of cells.

A plan to give federal funding to embryonic stem cell research has been delayed on the president's orders.

Some groups oppose the research because obtaining embryonic stem cells requires the death of a human embryo. These groups believe that adult stem cells, which can be isolated without the death of an embryo, should be studied instead.

Many researchers, however, believe the embryonic stem cells hold greater promise for treating disease using techniques similar to that reported by Freed and his colleagues.

Freed said he favors federal support of all the types of stem cell research.

"We need to find out which is the best source for treating any particular condition," he said. "All of the stem cell possibilities need to be tested."

Using a technique similar to one used for Parkinson's disease, researchers now are exploring ways to correct a brain disorder before birth.

Freed said the technique, years away from being ready for human clinical trials, holds promise for treating diseases of the brain that develop because of flawed brain cells.

He said an example would be Tay-Sachs disease, an inherited enzyme deficiency disorder in which a child is born normally, but has brain failure in years after birth.

The disorder occurs in about one out every 3,600 children born to European Jewish families and to French-Canadian families. It leads to mental retardation, blindness and death by the age of 4.

Freed said that in theory, injections of healthy neural stem cells could supplant the cells whose flaws cause Tay-Sachs and give the brain sufficient enzymes to develop normally after birth.

Dr. Larry Goldstein, a stem cell researcher at the University of California, San Diego, said the work "establishes some important properties of these cells and shows that they can engraft and colonize and migrate" within the brain.

In the study, the researchers isolated neural stem cells from a human fetus that came from an elective abortion. The cells were cultured until they numbered several million. Then they were injected into the developing brain of a monkey fetus at three months gestational age.

The monkey fetus was carried for another month and then removed by Caesarean section. The brain then was analyzed.

"The remarkable thing we found is that the stem cells we put in did not produce a glob of cells in one place in the brain," Freed said. "Instead, they distributed themselves around the fluid-filled spaces and went into an orderly migration to the areas of the brain that were under development."

In effect, the injected cells became an active, participating part of the young brain.