Senate Majority Leader Bill Frist bemoaned restrictions on federal support for stem cell research while opponents of such increased taxpayer financing argued that such a policy would be immoral.

With such seemingly insurmountable positions did senators reopen floor debate Monday on the politically and emotionally divisive issue. The newest debate sets up a showdown with President Bush, who vehemently opposes funding and likely will cast the first veto of his presidency.

The White House has shown no willingness to stray from the position that Bush took five years ago, when he halted government funding of any new embryonic stem cell research, a practice he called immoral. Bush said that 78 stem cell lines existed on which research could continue. But in the years since then, scientists have found that number to be far lower.

The Senate is expected to pass the bill Tuesday afternoon and Bush is expected to veto it Wednesday. The House is expected to try to override the veto as early as Wednesday, but support for the bill is expected to fall short of the required two-thirds majority.

That the debate is happening at all is the result of a deal brokered by Frist, who broke a yearlong standoff between supporters and opponents of the legislation. To satisfy opponents and clear objections blocking the debate, Frist also is allowing votes on two related bills. One, sponsored by Sen. Rick Santorum, R-Pa., would encourage study on stem cells derived from sources other than embryos. The other, sponsored by Santorum and Sen. Sam Brownback, R-Kan., would ban so-called "fetal farming," the possibility of developing fetuses and aborting them for scientific purposes.

Those two bills are uncontroversial. The House is expected to approve them Tuesday by voice vote, and Bush is expected to sign them.

But the bill lifting Bush's 2001 restrictions on federal funding for embryonic stem cell research is highly controversial and emotional because many scientists say the process holds the most promise for curing diseases that afflict millions of people.

"I feel that the limit on cell lines available for federally funded research is too restrictive," Frist said on the Senate floor Monday.

Senate Judiciary Committee Chairman Arlen Specter emphasized that the bill would only use embryos derived from fertility treatments that would otherwise be discarded. He compared opposition to the bill to historical resistance to research that led to such landmark advances as vaccinations against disease and space travel, "to show how attitudes at different times in retrospect look foolish, look absolutely ridiculous."

"There is just no sensible, logical reason why we would not make use of stem cell research," said Specter, R-Pa.

Opponents say the advance of science is not worth destroying human life. They believe that embryonic stem cell research is immoral because the process of extracting the all-purpose stem cells destroys a fertilized embryo that is a few days old.

"The government should not be in the business of funding this ethically troubling research with taxpayer dollars," Brownback said, adding that using embryos for such research amounts to "treating humans as raw material."

"It is immoral for us to do it," he added.

"I do not believe taxpayer dollars should support research that destroys human life," seconded Santorum said in a statement.

The wild card is the number of Senate supporters the legislation will win in Tuesday's tally. Vote-counters on both sides expect at least 60 supporters, the number required to pass. But whether the legislation can display the crucial veto-proof 67 is unknown. House supporters say a veto-proof margin in the Senate might inspire one in the House, though that is unlikely.

That chamber fell 50 votes short of that threshold last year, when it passed the bill 238-194.