But opponents of human embryonic stem cell research object to the work because extracting the stem cells destroys the embryo, which they regard as a human life.
Bush sought a compromise by allowing federal money to fund work on only cell lines that already exist and for which human embryos already had been destroyed.
In making his Aug. 9 announcement, Bush said that the National Institutes of Health had identified about 60 different stem cell lines. NIH has been working with companies that have them to set up a registry of the lines and draft a process for making the cells available to federally funded researchers.
But some scientists have questioned NIH's estimate of 60 lines, as well as the viability of the cells.
Many of the existing lines available under Bush's policy have been grown in the laboratory using mouse cells, which might make them unsuitable for human transplantation or subject to tighter controls imposed by the Food and Drug Administration, the Washington Post reported Friday.
Bush, asked at a news conference Friday if he knew about the mouse relationship before making his decision, said: "The NIH came into the Oval Office and they looked me right in the eye and they said: 'We think there is ample stem cells . . . to determine whether or not this embryonic stem cell research will work or not.' "