By teeing up a public battle over abortion in the health care bill now before the Senate, congressional Democrats could be risking more than just the fate of the legislation.

Hanging in the balance are millions of Catholic swing voters who moveddecisively to the Democrats in 2008 and who could shift away just asreadily in 2010.

According to exit polls, President Barack Obama won the support of 53percent of Catholic voters, a seven-point increase over the showing ofthe Democrats’ 2004 nominee, Sen. John Kerry (D-Mass.), a Catholic.Among Latino Catholics, who are often more conservative than theirwhite counterparts on social issues, Obama did even better, winningmore than two-thirds of their support, a 14-point improvement overKerry’s totals, according to an analysis by the Pew Research Center.

Those gains will be at risk if a polarizing abortion fight takes place in the Senate.

“There could be political repercussions in the election. It could beharder for the Democrats to keep those Catholics voters they gained andthey may put some of their members at risk,” said John Green, areligion and politics expert at the Bliss Institute at the Universityof Akron.

Moreover, said Green, Catholics are a constituency that backs thereform effort itself. “To alienate them on abortion could be toalienate them on health care reform,” he said.

The abortion issue, practically dormant during the 2008 campaign, wasreignited in the last hours of the health care debate in the Housebecause of an amendment offered by Rep. Bart Stupak(D-Mich.) that would prohibit the use of federal subsidies to pay forinsurance that covers abortion, except in the cases of rape, incest orwhen the life of the mother is threatened. 

The amendment, after heavy lobbying by the Catholic Church, eventuallypassed despite the furious objection of the abortion rights advocateswho have long been a key part of the Democratic base. Now the fightgoes to the Senate, where there will be a sharp division on the issuebetween party liberals and moderates.

Already it’s become an issue in the primary to choose a Democraticcandidate for the Massachusetts Senate seat of the late Ted Kennedy.

In a local television interview, one of the candidates, state AttorneyGeneral Martha Coakley, said that if she had been in the Senate shewould have killed the health care reform bill rather than support theStupak amendment.

One of her opponents, Rep. Michael Capuano, defended his House vote forthe bill by saying he wanted to keep the reform effort moving. But hevowed to vote against a final bill if it still contains the abortionfunding amendment.

In the neighboring and equally Democratic and Catholic state of RhodeIsland, the abortion amendment has played out another way. ProvidenceBishop Thomas Tobin, an outspoken critic of prominent Catholicpoliticians he believes are acting against church tenets, is engaged ina public feud with Democratic Rep. Patrick Kennedy, who voted againstthe Stupak amendment.

Anger over the church’s lobbying for the amendment prompted Rep. LynnWoolsey (D-Calif.), an abortions rights supporter, to call for anInternal Revenue Service investigation of the church’s tax status.

It’s a hollow threat. No law prohibits religious organizations fromlobbying Congress, provided the bulk of their budget expenditures arespent on other programs.

But the Woolsey retaliatory attack, published in POLITICO, generatedfresh headlines about the dispute and could drive a deeper wedgebetween the party and a key electoral constituency.

Tad Devine, a Democratic political consultant, said the party would be better off downplaying the disagreement.

“Voters who consider themselves Catholic are able to see the churchteachings in ways that can be pro-Democratic Party or pro-RepublicanParty,” said Devine, noting that the church is also a strong advocatefor immigrants in the health care debate.

Butsmoothing over the conflict isn’t likely to become an option. In fact,Senate Majority Leader Harry Reid (D-Nev.) is just now surveying hismembers to measure passions on the issue, a spokesman said.

Sen. Ben Nelson, an abortion rights opponent, has said language banningtaxpayer-backed abortion coverage is essential to winning his support.But a spokesman for the Nebraska Democrat told POLITICO Thursday thathe has no plans now to introduce an amendment and he is not wedded tothe exact wording in the House bill.

Sen. Bob Casey (D-Pa.), who also opposes abortion rights, saidlegislation should contain “strong language” to prohibit federal fundsfrom being used to pay for abortion insurance coverage. Beyond that,however, he hasn’t said what his intentions are since Reid has yet tounveil a final bill.

Meanwhile, advocates on both sides are gearing up for a major showdown over the issue.

“When the Senate takes up the issue, it will be in the light of day,with the nations eyes upon them,” said Douglas Johnson, chief lobbyistfor the National Right to Life Committee.

“We’ve read in the papers that Harry Reid will put a public plan in hisbill. I suspect it will have phony language that will allow for usingpublic funds for abortion,” he added.

For weeks, priests have used Sunday sermons to urge parishioners to contact their representatives and ask them to back amendments blocking federally-backed abortion coverage.

They have also put Republicans on notice that the church won’t tolerateattempts to use procedural tactics to scuttle such amendments – as wascontemplated by House Republicans.

But even if the abortion language is adopted, it’s unclear if theCatholic Church ultimately will endorse the health reform legislation.The U.S. Conference of Catholic Bishops, the church’s main lobbyingarm, declined comment for this article.

In a statement released after the House adopted the Stupak amendment,Chicago’s Cardinal Francis George, president of the conference, praisedthe vote but raised other concerns that could spark debate on otherdivisive, social issues.

For instance, George noted the conference remained “deeply concernedthat immigrants be treated fairly and not lose the health care coveragethey now have.”

Progressives are also girding for the Senate fight.

On Monday, the Religious Coalition for Reproductive Choice, whichincludes an array of Protestant, Jewish and some Catholic members willhold a news conference with First Amendment advocates to push backagainst opponents of abortion rights.

The coalition will urge Congress to pass a final health care bill ensures abortions are “safe, legal and accessible” and one that “respects diverse religious beliefs.”