* Batches already in existence may be reviewed

* NIH says rules reflect broad public support (Adds reaction from Republican opponent, paragraph 9)

WASHINGTON, July 6 (Reuters) – The U.S. government released new rules on Monday governing federally funded research on human embryonic stem cells, loosening some ethical requirements that scientists said could have cost them a decade of work.

The rules, which take effect on Tuesday, keep many existing restrictions on the research. U.S. federal funds may still not be used to actually make the cells using human embryos — only to work with the cells after someone else has made them.

But the National Institutes of Health, which issued the rules, eased some of the measures in the initial guidelines drawn up in March, including the so-called “informed consent” requirements meant to ensure that people who donated embryos for research knew exactly what they might be used for.

“We allow a case-by-case review,” acting NIH director Dr. Raynard Kington told reporters in a telephone briefing.

In March, President Barack Obama lifted restrictions on human embryonic stem cell research that had been put in place by his predecessor, former president George W. Bush and asked the NIH to draw up new guidelines.

Stem cell company stocks did not move much on news of the new rules, in part because the changes mostly affect academic researchers who rely on federal funding for their work.

The NIH guidelines take into account many of the arguments put forward during nearly 10 years of debate over how best to use the potential of human embryonic stem cells, which have the power to give rise to all the cells and tissues in the body and which supporters hope can transform medicine.

Opponents say it is wrong to destroy human embryos for any reason.

“The administration’s decision to dramatically expand the number of stem cell lines derived from human embryos and create incentives for the destruction of human life is a provocative step beyond what the president proposed just months ago and yet another sign that he has quickly retreated from his promise to be a president for all Americans,” House of Representatives Republican leader John Boehner said in a statement.

However, over the years Congress reached a middle ground, with many social conservatives such as Utah Republican Senator Orrin Hatch supporting such research if it used embryos left over at fertility clinics.

BROAD PUBLIC SUPPORT

“The guidelines reflect the broad public support for federal funding of research using human embryonic stem cells created from such embryos based on wide and diverse debate on the topic in Congress and elsewhere,” the new rules say.

They limit such research to these in vitro fertilization or IVF leftovers but also loosen restrictions on using human embryonic stem cells made in other countries.

In April when the initial guidelines were published some scientists said the “informed consent” rules on educating embryo donors were so strict that they might force labs to discard valuable stem cell batches, called lines.

“The draft guidelines that were released were so restrictive that I feared the vast majority of lines would be excluded,” Dr. George Daley of Harvard University in Massachusetts said in a telephone interview. He said the revised rules answer his concerns.

“It is the most that the administration can offer under current law,” said Dr. John Gearhart, a stem cell expert at the University of Pennsylvania. “There are many ‘new’ cell lines that have exceptional properties and have been maintained under better conditions that will meet the criteria of use.”

The rules create in effect the first official federal oversight of human embryonic stem cell research, the American Society for Reproductive Medicine said.

Following are some facts about stem cells:

* Stem cells are the body’s master cells, the source of all cells and tissue, including brain, blood, heart, bones and muscles.

* Embryonic stem cells come from days-old embryos and can produce any type of cell in the body.

* Scientists generally harvest embryonic stem cells from embryos left over after in vitro fertilization attempts at fertility clinics. They can also be produced using cloning technology but the new U.S. rules allow for federal funding only of work on surplus IVF embryos.

* Scientists hope to harness the transformational qualities of stem cells to treat a variety of diseases, including injuries, cancer and cystic fibrosis.

* The issue is controversial because some people believe the destruction of any human embryo is wrong.

* Several companies are pursuing stem cell research including Geron Corp. which last week teamed up with General Electric Co to use stem cells to test new drugs for toxicity.

* Other companies involved in stem cell research include Stemcells Inc., Advanced Cell Technology, NeuralStem, Aastrom Biosciences Inc., Reneuron Group Plc., Thermogenesis, Osiris Therapeutics Inc, Neostem Inc., Cytori Therapeutics Inc., iZumi Bio Inc., and International Stem Cell Corporation.

*U.S. legislation called the Dickey Amendment forbids the use of federal funds for the creation or destruction of human embryos for research, but new U.S. policy allows federally funded researchers to work with cells someone else had taken from an embryo.

* The issue does not fall clearly along party lines and some conservative Republicans who oppose abortion have backed broader federal funding of embryonic stem cell research for years.

* Britain, Belgium, Sweden, Canada and New Zealand encourage embryonic stem cell research. Austria, Lithuania and Poland have laws banning most human embryonic stem cell research.

* Researchers have discovered how to make embryonic-like cells from ordinary cells, called induced pluripotent stem cells. Opponents of embryonic stem cell research say research can focus on this field, but most scientists agree that all approaches must be pursued.