WASHINGTON -- U.S. Sen. Arlen Specter yesterday renewed his call for a significant expansion of federal funding for embryonic stem-cell research, a bill that fellow Pennsylvania Sen. Bob Casey will oppose when it comes up for a vote this week.

The split between the state's two senators could kill the bill's chance of becoming law in the near future.

President Bush has promised to block the legislation, just as he did last year, when he issued the only veto of his presidency. The Senate would need at least 67 votes to override a new veto, and Mr. Casey's stance may prevent that. The freshman Democrat, who ran on a pro-life platform in last year's campaign, is against research that extracts stem cells by destroying human embryos.

Supporters argue that the research has the potential to develop treatments for a range of medical conditions, including diabetes, Parkinson's and spinal cord injuries.

"I have listened carefully, especially to those whose loved ones are suffering from serious diseases and disabilities, and who disagree with my position," Mr. Casey said in a statement. "I deeply respect their views and hope they can come to understand mine."

The legislation still has broad, bipartisan support. Mr. Specter, a Republican and longtime advocate for expanded stem-cell research, yesterday joined several colleagues of both parties, including Sen. Edward Kennedy, D-Mass., and Sen. Orrin Hatch, R-Utah, to promote the bill.

Mr. Specter also spoke passionately on the Senate floor, citing the diseases of friends and colleagues and arguing that the federal government has wavered in its commitment in the "war on cancer."

Mr. Specter cited his own recent battle with Hodgkin's disease, a cancer of the lymph system. "That trauma and that illness could have been prevented," he said.

Opponents argue that, by destroying human embryos, the research destroys life.

In August 2001, the Bush administration proposed a compromise, authorizing limited funding for stem-cell lines that were already in existence.

But critics of that policy say the existing lines are too few in number to allow meaningful research, and they point to the tens of thousands of embryos that already are discarded each year by fertility clinics across the country.

"If any of these embryonic stem cells could be used to produce life, none of us would advocate the research," Mr. Specter said. "But they will not be used to produce life."

Last year, the House and Senate both approved a bill that would have expanded the research. The president vetoed it, warning that the legislation crossed a "moral boundary."

Advocates hoped that the Democratic victory in November would change the equation. In January, the House passed a new bill, with 37 Republicans joining 216 Democrats. The tally in that chamber also was short of the margin to override a veto.

Mr. Casey has been the target of lobbying campaigns from both sides.

"Given his campaign commitment to oppose federal funding for embryonic stem-cell research, and given the role pro-life Pennsylvanians played in electing him, you would think the Stem Cell Research Enhancement Act of 2007 would be a no-brainer for Casey," Charmaine Yoest, vice president of communications for the Family Research Council, wrote in an opinion piece in the Philadelphia Inquirer last month.

Mr. Casey has said he supports alternative types of research using adult stem cells or cells taken from the amniotic fluid of pregnant women. His spokesman yesterday said the senator also supports another bill, put forward by Sen. Johnny Isakson, R-Ga., that would restrict funding to research using embryos that no longer have the potential to develop into human beings. But supporters of the main stem-cell bill argue that Mr. Isakson's attempt at compromise doesn't go far enough.

Even if the votes aren't there now, Mr. Specter argues that major stem-cell legislation has overwhelming support and eventually will become law. "The longer it is delayed," he said, "the more people will suffer and die from these maladies."