WASHINGTON – Congress opens a second showdown with President Bush over embryonic stem cells this week, with Democrats now in charge and hoping to push through an expansion of taxpayer-funded research into the controversial cells.

Complicating that question: There are different types of stem cells. Fetal stem cells found floating in amniotic fluid are the latest to make headlines, a finding cited by foes of the embryonic stem-cell legislation that is certain to pass the House on Thursday.

“We don’t have to split the nation on this if we’ve got an alternative,” said Rep. Phil Gingrey, R-Ga., an obstetrician who opposes embryonic stem-cell research because culling the cells from 5-day-old embryos destroys them.

“What we hope is that scientists will find ways to unlock the promise of stem cells without having to force people into the choice of claiming a human life in so doing,” White House spokesman Tony Snow said Monday, making clear the president hasn’t changed his stand since vetoing an identical bill to expand embryonic stem-cell research just six months ago.

Polls show a majority of Americans support embryonic stem-cell research, and Democrats say the public demanded action by casting ballots for stem-cell supporters in the November election.

Focusing on preliminary “alternatives” like the amniotic stem cells won’t fool that public, said Sen. Tom Harkin, D-Iowa.

“If we truly want to cure and treat diseases that afflict so many people in this country, our nation’s top scientists should be allowed to pursue stem-cell research of all kinds, be it embryonic, adult or amniotic,” he said.

The scientific community stands firm that research, not ideology, must determine stem cells’ true promise – and that embryonic stem cells so far are backed by the most promising evidence that one day they might be used to grow replacements for damaged tissue, such as new insulin-producing cells for diabetics or new nerve connections to restore movement after spinal injury.

“Let’s let the laboratories worldwide figure out which ones are the best for the task at hand, and that’s discovering treatments and cures for people who need them,” said bioethicist Christopher Scott, who heads the Stanford Program on Stem Cells and Society.

Embryonic stem cells are able to morph into any of the more than 220 cell types that make up the human body. They typically are culled from fertility-clinic leftovers otherwise destined to be thrown away.

But because the culling kills the embryos, Bush on Aug. 9, 2001, restricted government funding to research using only the embryonic stem cell lines then in existence, groups of stem cells kept alive and propagating in lab dishes.

The problem: There are only about 21 of those lines available for study, most created in ways that preclude use in humans. At least 300 more lines now are available that many scientists insist are better suited for implantation into sick people.

The new legislation wouldn’t fund the creation of stem cell lines and hence any embryo destruction, but it would allow the National Institutes of Health to fund research using those already-existing newer stem cell lines.

Fetuses also shed stem cells into amniotic fluid, allowing scientists to cull those cells harmlessly when pregnant women undergo birth-defect tests. Those cells can turn into several different tissue types, but don’t yet seem as flexible as embryonic ones.

And scientists are working on ways to cull stem cells from embryos without killing them.