The U.S. Senate Tuesday is expected to approve federal funding for expanded embryonic stem cell research, despite a veto threat from President Bush who opposes the idea on moral grounds.

On the eve of the vote, senators engaged in emotional debate on embryonic stem cell research, raising matters of life and death and highlighting personal stories of Americans who could be affected by the issue.

Scientists and other advocates of embryonic stem cell research say it has the potential to treat illnesses such as diabetes, Parkinson's disease and cancer. They note that embryonic stem cells can form different tissue types found in the human body, and thus have the potential to replace damaged or diseased organs.

Sen. Tom Harkin, (l), and Sen. Arlen Specter, take part in a Capitol Hill news conference on stem cell research, July 17, 2006

Senator Arlen Specter, a Pennsylvania Republican, said "the debate on embryonic stem cell research is as important as any issue which has ever been before the United States Senate. We are on the threshold of being in a position to save tens of thousands of lives and save tens of thousands of people from extensive human suffering."

Specter cites public opinion polls that show a majority of Americans support such research. He says the legislation before the Senate would involve only embryos that come from fertility treatments that would otherwise be discarded.

Joining Specter at a news conference was former Defense Secretary Frank Carlucci, who suffers from Parkinson's disease and serves on the board of the advocacy group, the Parkinson's Action Network.

"We do not know for certain if stem cell research can lead to a cure for Parkinson's, but it will certainly help our understanding of what causes the disease and what its evolution is. Many do think it can lead to a reversal of Parkinson's unrelenting degeneration," he said.

Most Senate Democrats support the legislation. Senator Dianne Feinstein of California says U.S. scientists are going overseas to conduct human embryonic research because of the restrictions in this country.

"Researchers are attracted by the federal funding provided in at least 10 other nations: Germany, Finland, France, Sweden, the United Kingdom, South Korea, Singapore, Israel, China and Australia. These investments total hundreds of millions of dollars that are already producing tangible progress," she said.

The Republican majority in the Senate is divided on the issue. Opponents, including those who make up the party's conservative base, argue that embryonic stem cell research amounts to the taking of human life because an embryo is destroyed in the process.

"It is immoral to destroy the youngest of human lives for research purposes. We do not need to do it," said Senator Sam Brownback, a Kansas Republican.

Brownback spoke at a news conference, where he was joined by Steve Johnson of Pennsylvania.

Johnson and his wife adopted a daughter who came from a donated embryo at a fertility clinic. Johnson is also wheel chair-bound, as a result of a bicycle accident that damaged his spinal cord.

Johnson said he would like to be cured of his affliction, but not if it comes at the expense of destroying an embryo.

"Would I kill my daughter so I could walk again? Should I have an incremental benefit at the expense of someone else's son or daughter? Of course not. The answer is no," he said.

President Bush also opposes the Senate measure and has vowed to veto it. In 2001 the president limited government funding for stem cell research to human embryonic stem cell lines already in existence, citing religious reasons.

The Senate bill appears to have the 60 votes needed for passage, but it is unclear whether there is the necessary 67 votes - or two-thirds majority of the 100-member Senate - to overturn a veto.

The measure passed the House of Representatives last year, but it fell 50 votes short of the two-thirds majority needed to override a veto.

Republicans are concerned about the political impact a presidential veto could have on their reelection chances in November. So the Senate will be voting on two other stem-cell related bills that President Bush has signaled he could sign: one would encourage study on stem cells derived from sources other than embryos and the other would ban the production of embryos solely for stem cell harvest.