WASHINGTON-The Bush administration acknowledged Wednesday that fewer than half the stem cell lines approved for federal funding are fully developed and ready for researchers.

Health and Human Services Secretary Tommy Thompson said that more cell lines will probably be ready by the time federal grants are issued next year. But even if they aren’t, he said, two dozen cell lines are enough to get the science moving. Of the 64 cell lines approved for research, Thompson said 24 or 25 are ready. The others are in earlier stages of development..

Sen. Arlen Specter, R-Pa.and others have said they will try to lift the restrictions, although Bush appears to have satisfied enough people to keep Congress from acting.

Bush’s decision permits research only on cells coming from embryos processed before the cutoff date. He also required that the cells be derived from embryos considered surplus at fertility clinics and which were donated for research, by couples who were fully informed about the process.