WASHINGTON -- Near the top of the new Democratic congressional majority's agenda is passage of federal embryonic stem cell research legislation vetoed last year by President Bush, a measure that will answer a major question. There is no doubt the new bill will pass both houses of Congress. What remains in doubt are the votes to be cast by newly elected Democrats who campaigned as pro-life advocates, particularly Sen. Bob Casey Jr.

Outside the boundaries of his state of Pennsylvania, Casey is best known as the son of the Democrat most revered in the pro-life movement: the late Gov. Robert Casey. Denied the podium at the 1992 Democratic national convention because of anti-abortion views, the elder Casey planned a serious independent campaign for president before being stopped by poor health. But will the son, less ardent a pro-lifer than the father, vote against the stem cell research bill as he once promised during the campaign? Will seven self-described pro-life Democrats newly elected to the House do the same?

Casey's vote may determine whether Bush's second veto is overridden by the Senate. The House will probably sustain a veto, with or without help from the seven Democrats. But apart from the stem cell bill, at stake is whether pro-lifers have any place in today's Democratic Party. Certainly, that small fraction will be under intense pressure from party leaders.

Casey won a nationally spotlighted contest, defeating eminent Republican conservative Sen. Rick Santorum. He cut into Santorum's conservative base by winning 36 percent of the state's hard pro-life vote.

The only recorded statement by Casey on stem cell research came in an interview on the Catholic website IgnatiusInsight.com on July 29, 2005: "I am and I have always been pro-life. I support the current [Bush administration] policy on embryonic stem cell research and would oppose the Castle bill to expand federal support of embryonic stem cell research."

That referred to the bill sponsored by Republican Rep. Mike Castle of Delaware that died in 2006 when the House sustained Bush's veto. But a new version is likely to be considered now in the Senate, where a supporter -- then Majority Leader Bill Frist -- conceded in a private session last year that the Castle bill was flawed and must be rewritten.

So, would Casey oppose any legislation that authorizes federally financed stem cell research on "left over" embryos from in-vitro fertilization clinics, as the Castle bill did? Casey the younger plays his cards close to his vest, and my efforts to get a commitment one way or another from the new senator or an aide were unavailing.

This is the arithmetic in the Senate, where a vetoed bill will go first. It would take 33 senators to sustain a Bush veto, if ailing Democratic Sen. Tim Johnson (S.D.) is unable to vote. Of the 36 Republicans who voted against the Castle bill, five were defeated for re-election: Santorum, George Allen in Virginia, Conrad Burns in Montana, Mike DeWine in Ohio and James Talent in Missouri. Sen. Ben Nelson (Neb.) was the only Senate Democrat who voted no last year, and that means one more Democrat would be needed this year. Casey's vote could be central.

The House sustained last year's veto by a 50-vote margin. Thirteen of those members were defeated in November. So, even if there are Republican defections, the burden will not fall on seven avowedly pro-life Democrats newly elected to the House: Heath Shuler (N.C.), Charlie Wilson (Ohio), Joe Donnelly (Ind.), Brad Ellsworth (Ind.), Baron Hill (Ind.), Jason Altmire (Pa.) and Chris Carney (Pa.).

With Speaker Nancy Pelosi putting this legislation on her 100-hour list, these pro-life House Democrats, nevertheless, will be under intense pressure, as will Nelson, Sen. Jon Tester, a pro-lifer who defeated Burns in Montana last year, and Bobby Casey.

Casey was embraced by pro-choice Democrats -- led by Sen. Chuck Schumer, chairman of the Democratic Senatorial Campaign Committee, and Pennsylvania Gov. Ed Rendell, as the best bet against Santorum. But they may not have bargained on Casey opposing them on the central party issue of stem cell research. The question of how much of a pro-lifer Casey is or can be in the 21st-century Democratic Party may be answered soon.