DENVER | Sen. Joseph R. Biden Jr. arrived at the Democratic National Convention on Monday amid rumblings over whether his pro-choice Catholicism would help or hurt the Democratic ticket.
An Irish-Catholic from a working-class upbringing, Mr. Biden won the nod as presumptive presidential nominee Barack Obama's running mate in part because of his appeal to blue-collar Catholics, the same voters who swung during the primary for Sen. Hillary Rodham Clinton of New York.
Although he represents Delaware in the Senate, Mr. Biden grew up in Pennsylvania, a must-win state for Democrats in November.
But the party's hopes of winning the critical Catholic vote took a hit Sunday when Archbishop Charles Chaput of Denver said Mr. Biden should avoid taking Communion as a result of his pro-choice stand on abortion.
Archbishop Chaput, who was scheduled to lead a pro-life candlelight vigil Monday night here in front of Planned Parenthood, called Mr. Biden's support for abortion rights "seriously wrong," said archdiocese spokeswoman Jeanette De Melo.
"I certainly presume his good will and integrity," said the archbishop, "and I presume that his integrity will lead him to refrain from presenting himself for Communion if he supports a false 'right' to abortion."
The archbishop, who was not invited to speak at any convention events in what appeared to be a deliberate snub, told the Associated Press that he would like to speak privately with Mr. Biden.
The debate underscored what has emerged as a central theme of this year's convention: the tension between the Democratic Party's renewed outreach to religious voters and its long-standing support for unfettered access to abortion.
At a panel discussion Monday sponsored by Google on "The Shifting Faith Vote: What It Means for the Election," panelists said that concerns over social issues, such as poverty, are moving some faith-based voters away from the Republican Party.
At the same time, they haven't aligned with the Democrats, primarily because of the abortion issue.
"The push for the Democratic Party is to have a new position on abortion," said Steve Waldman, editor of the religious Web site beliefnet.com. "When you look at Catholics and evangelicals, you see that they agree with 80 percent of what [Mr. Obama] says, but there's this stumbling block with abortion."
Whether pro-choice Catholics should take Communion became a major issue in 2004 during Democrat John Kerry's run for the presidency when more than a dozen bishops, including Archbishop Chaput, publicly asked the senator from Massachusetts not to present himself for the Eucharist.
Their stance may have given a boost to President Bush, who increased his share of the Catholic vote from 47 percent in 2000 to 52 percent in 2004.
Catholics, the nation's largest religious voting bloc, represent 26 percent of the electorate. Alexia Kelley, executive director of Catholics in Alliance for the Common Good, said that 11 percent of those this year are considered "swing voters," more than in any recent election year.
Catholic advocacy groups didn't wait long before weighing in on the "wafer wars." The conservative Catholic group Fidelis condemned the selection of Mr. Biden.
"Now everywhere Biden campaigns, we'll have this question of whether a pro-abortion Catholic can receive Communion. ... Selecting a pro-abortion Catholic is a slap in the face to Catholic voters," said Fidelis President Brian Burch.
• Julia Duin reported from Washington.