Federal researchers asked by President Bush for more information about embryonic stem cell research refrained from recommending federal support for the research, but said it should be included among the possible avenues for treating disease.

Some critics dismissed the report for failing to "take ethics into consideration," and an executive summary of a confidential report from the National Institutes of Health, obtained by The Associated Press, focused on science. 

"During the next several years, it will be important to compare embryonic stem cells and adult stem cells in terms of their ability to proliferate, differentiate, survive and function after transplant, and avoid immune rejection," said the report.

The report was to be presented formally at a Senate subcommittee hearing Wednesday. The White House received a copy Tuesday, said presidential spokesman Scott McClellan.

"The report is one component of the scientific, ethical and legal issues involved," McClellan said. "The president intends to look at it in that context."

Bush is weighing whether to allow federal funding of embryonic stem cell research, which some oppose because isolating the cells requires the death of a human embryo.

Scientists believe they can learn to direct the development of embryonic stem cells to grow mature cells or tissues that could be used to treat disease and disorders such as Alzheimer's disease, Parkinson's disease, diabetes and spinal cord injuries.

Opponents of the research favor using adult stem cells, which are taken from mature organs and then manipulated in the lab.

The federal researchers said embryonic stem cells can develop into all types of cells and tissue and they said this flexibility might be lacking in so-called "adult" stem cells taken from mature tissue. However, the report concludes, "the answers clearly lie in conducting more research."

A consistent theme of the report is that more research is needed before any firm, scientific conclusion can be reached on the relative medical value of the stem cell types.

Nonetheless, opposing sides are contending the report validates their argument.

"They don't take ethics into consideration, they ignore some of the recent studies that show adult stem cells can change and proliferate, and still they conclude that adult stem cells have amazing potential," said Rep. Chris Smith, R-N.J., who opposes embryonic stem cell research.

To Sen. Tom Harkin, D-Iowa, the report says that in some cases, "embryonic stem cells are more promising than adult stem cells."

Harkin, whose Senate panel oversees federal health spending, would push for legislation allowing the stem cell funding if Bush doesn't approve it.

The Associated Press contributed to this report.