WASHINGTON -- U.S. Sen. Arlen Specter today called for the federal government to vastly expand funding for embryonic stem cell research, while Sen. Bob Casey has said he won't support a bill coming up before the Senate for a vote this week.

President Bush vetoed stem cell legislation last year, and supporters hoped the new Democratic Congress would have enough votes to override the veto. But Mr. Casey's position makes it harder for them to reach the 67-vote threshold in the Senate.

"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, a Democrat, said yesterday. "I deeply respect their views and hope they can come to understand mine."

Mr. Specter, a Republican and longtime supporter of the research, spoke passionately on the Senate floor, bringing up 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, noting that the federal government had promised to wage a "war against cancer" three decades ago.

Opponents argue that the research destroys life to extract stem cells from human embryos, but supporters of the bill before the Senate say it would restrict research to embryos that would be discarded by fertility clinics.

"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."