WASHINGTON -- Fewer than half the embryonic stem cell lines approved for federal funding are ready for research, the Bush administration admitted Wednesday as it defended the president's restrictions to skeptics on Capitol Hill.

Health and Human Services Secretary Tommy Thompson said he expects more of the existing cell lines to be fully developed by the time federal grants are issued next year. Even if they aren't, he said, two dozen cell lines are enough to get the science moving.

Thompson also announced the administration had reached its first -- and most important -- agreement on patent issues that will allow research to go forward. Under the agreement, the Wisconsin Alumni Research Foundation, which holds patents on the method of isolating cells, will allow widespread use for research. The foundation still stands to make money on any treatments that someday result from the research.

"Our challenge now is to move beyond the halls of debate and into the labs of science," Thompson told the Senate Health, Education, Labor and Pensions Committee in the most extensive public debate since President Bush said he would allow limited federal funding for research using stem cells from human embryos.

Thompson faced clear skepticism from senators who argued the Bush policy will hamper researchers and delay treatments for millions of Americans who suffer from Parkinson's, Alzheimer's and other diseases. Scientists hope they can coax stem cells, which can develop into any sort of human tissue, into new cells to treat disease.

"It would be unacceptable to offer these patients and their families the promise of effective stem cell research but deny them the reality of it," said Sen. Edward Kennedy, D-Mass., the committee's chairman.

Kennedy called the Bush restrictions "very troublesome," but it remained unclear whether research proponents have sufficient support to overturn the Bush plan.

The research is controversial because the stem cells come from days-old embryos, typically those leftover from fertility treatments that would be destroyed. Despite this, some people believe it's morally wrong to use them for research.

Last month, Bush struck a middle ground, saying federal money could support this research but only on stem cell colonies in existence on Aug. 9, the date of his speech. Embryos already had been destroyed in such cell lines.

Since then, the administration has met criticism from research supporters who suspect the existing 64 stem cell lines will be inadequate, tainted or unavailable for use. Despite the misgivings, Thompson reiterated Wednesday that the administration will not reconsider financing research on stem cell lines developed after Aug. 9.

Among the chief objections of research proponents: Many of the lines -- colonies of cells each derived from single embryos -- are not yet fully developed and may never be useful to researchers.

"Many of the lines cited are not really viable or robust or usable," said Sen. Arlen Specter, R-Pa.

An Associated Press survey of the organizations that have the cell lines found researchers considered just 20 of them to be fully developed.

Thompson was more bullish, estimating that about 24 or 25 of the existing stem cell lines are fully developed and ready for research, with others in earlier stages of development. "We're confident there is enough, and we're confident the private sector will fill the voids where there are any voids," he said.

Another concern: Many of the existing lines may have been contaminated by mouse cells, which are needed to help nurture stem cells after they are extracted from embryos. If proper safeguards were not taken, treatments developed using such cells might be unable to win Food and Drug Administration approval.

Thompson said he does not know how many of the lines might be contaminated but suggested it might not matter. Federally funded research may simply lay groundwork for future privately funded work to develop the treatments, he said.

His announcement of the agreement with the Wisconsin foundation helped put to rest other concerns that problems with patents would prevent researchers around the country from moving ahead.

Under the deal, reached Tuesday, researchers will have access to five stem cell lines owned by the University of Wisconsin, and the university will allow researchers to use its methods of extracting cells without compensation. Thompson, a 14-year Wisconsin governor, did not participate in the negotiations.

This deal applies only to basic research that precedes commercial applications. Anyone who develops a treatment with moneymaking potential will have to negotiate a separate deal to share profits with the foundation. So it's in Wisconsin's financial interest to see research move ahead quickly.

HHS still has to negotiate similar agreements with the nine other universities and companies in the United States and elsewhere that own existing stem cell lines.

------

Associated Press writer Joe Verrengia in Denver contributed to this report.

------

On the Net: Health, Education, Labor and Pensions Committee: http://labor.senate.gov/