The Bush administration is being pressed by some Republicans to support research that uses stem cells from human embryos, a practice opposed by a number of abortion foes because it involves embryos discarded by fertility clinics.

Several Republicans, including long-term abortion opponent Sen. Orrin Hatch of Utah, contend that such research is legal, ethical and scientifically valuable.

"I have rarely, if ever, observed such genuine excitement for the prospects of future progress than is presented by embryonic stem cell research," Hatch wrote in a letter to President Bush.

He added that other GOP abortion opponents -- like Sens. Strom Thurmond of South Carolina, Gordon Smith of Oregon, and Connie Mack of Florida -- believe Bush should "lead the way for this vital research."

In a separate letter to the president, moderate Sen. Susan Collins of Maine, said, "Stem cell research holds tremendous potential to treat and even cure a vast array of diseases and conditions." She added that researchers agree that "it will take years of further study to determine the therapeutic potential of adult stem cells (taken from mature tissue)."

There's no immediate word on whether the administration has responded to the senators.

"The issue is being reviewed right now, and beyond that we have no comment," said Tony Jewell, a spokesman for Health and Human Services Secretary Tommy Thompson.

The department oversees federal spending on medical research.

Meanwhile, Bush administration officials on Wednesday stopped short of fully endorsing current plans to ban the cloning of human embryos for medical research. Some lawmakers in Congress have proposed a total ban on that practice and on any human cloning experiments or funding.

"We look forward to working with the Congress to prohibit morally offensive uses of cloning technology without stifling the development of important cell- and tissue-based therapies to combat human diseases," Claude Allen, a Thompson deputy, told the House Energy and Commerce Committee, which oversees health issues.

Stem cells are building blocks for all human tissue. The most versatile cells are derived from embryos discarded at fertility clinics, but some abortion opponents say it is wrong to use them for research.

Research proponents say the embryos are being destroyed anyway and that using them could lead to revolutionary treatments for Alzheimer's disease, diabetes, spinal cord injuries and other ailments.

Congress has barred federal money for research that destroys embryos. But late in the Clinton administration, officials decided that the National Institutes of Health could pay for research using cells that had been extracted by privately funded research.

Earlier this year, the new Bush administration suspended that policy, saying it needed time to review questions of scientific value and ethics. Abortion opponents have pressured the White House to permanently overrule the policy.

Another group of senators, most of them conservative, wrote a letter saying federal funding of any embryonic stem cell research should be blocked.

Thompson supported similar research in Wisconsin where he was governor. Since arriving in Washington, he has said he's mindful of conflicting views and is working to reach a compromise. So far, he hasn't provided details about a decision he says is coming in July.