RENEE MONTAGNE, host:

It's MORNING EDITION from NPR News. Good morning, I'm Renee Montagne.

STEVE INSKEEP, host:

And I'm Steve Inskeep. Welcome back.

This report may start out sounding like you've heard it before. The Senate is expected to pass legislation on stem cell research today. It would expand the number of embryonic stem cell lines eligible for federal research money. It's almost the same bill that passed last year. And just like last year, President Bush is expected to veto it if it reaches his desk.

Now here's what might be different. Democrats hope they might have the votes to override that veto, as NPR's David Welna reports.

DAVID WELNA: This time, there are several newly-elected Democrats backing this cause who replaced Republicans who'd opposed it. What's more, National Institutes of Health Director Elias Zerhouni last month broke with the White House on stem cells.

He told a Senate panel the nation would be better served if American scientists were given access to more embryonic stem cell lines than the couple of dozen that President Bush sanctioned nearly six years ago. Iowa Democrat Tom Harkin is the chief sponsor of the bill expanding such access. And he urged his colleagues to heed the NIH director's advice.

Senator TOM HARKIN (Democrat, Iowa): Now Dr. Zerhouni is the federal government's top scientist in the area of medical research. President Bush appointed him to be the director of the National Institutes of Health. So it took great courage on his part to say in public that we need to change direction on stem cell research, but he did so because it's the truth.

WELNA: There's broad public support for more stem cell research since it holds the promise of curing everything from Alzheimer's disease to juvenile diabetes. So a vote against Harkin's bill could hurt senators facing tough reelection bids next year.

One such senator is Minnesota Republican Norm Coleman. He's co-sponsoring a competing stem cell bill that senators leery about using human embryos can vote for later today. It, too, calls for more stem cell research, as long as it does not involved viable human embryos.

Senator NORM COLEMAN (Republican, Minnesota): Some would say it's not all we want, but we're moving the science forward. Let's do that. Hopefully, real hope will be given, and real cures ultimately will be found. And we'll have done in a way that that doesn't - have engaged the culture wars, but in the end, makes real progress with real science.

WELNA: Both stem cell bills are expected to easily pass with more than 60 votes. The big question is whether there's the two-thirds majority needed to override a presidential veto of the bill supporting more embryonic stem cell research.

California Democrat Dianne Feinstein called on groups backing it to pressure lawmakers.

Senator DIANNE FEINSTEIN (Democrat, California): We're very close to making a veto-proof bill. But it's really up to you - it's really up to your now coming forward and rallying people to call members in the Senate that might be turned around by the specific nature of this bill - the fact that it has passed the House once, the fact that we have something which is essentially as big a compromise as we can possibly make.

WELNA: That compromise involved adding language supporting other kinds of stem cell research as well. Still, Utah Republican Orrin Hatch, who backs the bill, says it did not help that Democrats made stem cell research a campaign issue last year.

Senator ORRIN HATCH (Republican, Utah): I tried to talk my colleagues into not making it political in the last election. I think that cost us. I think we would have probably 70 votes today if it hadn't been made political in the last election.

WELNA: But bill sponsor Harkin says that election had a big lesson for lawmakers - namely, that if they oppose expanding access to embryonic stem cells, they do so at their peril.

Sen. HARKIN: As you looked across the landscape, that was clear that the people voted last November for candidates who supported embryonic stem cell research - on both sides of the aisle, I might add. It wasn't necessary at one party or the other.

WELNA: Democrats concede, though, that while they may be within one vote of a veto-proof bill on the Senate, getting a similar two-thirds majority in the House will be much harder. And that's what it would take to override the presidential veto, threatened again yesterday by the White House.

David Welna, NPR News, the Capitol.

INSKEEP: Here's a bit of a timeline. The first embryonic stem cells were isolated in mice in 1981. It wasn't until 1998 that researchers managed to derive stem cells from human embryos, and you can follow key moments in the resulting ethical debate at npr.org. Transcript provided by NPR, Copyright NPR.