UPDATE 3-US stem cell research rules ease some restrictions

* Human embryonic stem cells must be clinic leftovers

* Batches already in existence may be reviewed

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

By Maggie Fox, Health and Science Editor

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.