WASHINGTON — In his first ceremonial appearance on U.S. soil, Pope Benedict XVI will be honored at a huge White House gathering this morning by a conservative Protestant president who courted and won a majority of Catholic votes in 2004 — the first Republican presidential candidate in a generation to do so.

But as a glance at heavily Catholic Rhode Island’s all-Democratic congressional delegation reveals, the very notion of a “Catholic vote” that hews to moral edicts from Rome is wrong-headed.

Nevertheless, Benedict’s visit is a major political and spiritual event in part because Catholics as a group have distinctive traits as citizens that make them a force in American politics — starting with the power of their numbers, 67 million, or roughly a quarter of the population.

Polling shows that Catholics are keenly attuned to where their church stands on moral issues with a political dimension, even if they are skeptical of church pronouncements. There are liberals who support embryonic stem cell research, for example, or conservatives who disagreed with then-Cardinal Joseph Ratinzger’s warnings against the U.S. invasion of Iraq.

When Benedict speaks, in other words, Catholics will tend to listen, even if he does not change their minds. So will other citizens who are interested in how the pope might shape the political discourse in a presidential election year.

“There is no such thing as a monolithic Catholic vote in the United States,” according to John C. Green of the Pew Forum on Religion and Public Life, an independent think tank in Washington.

“Even though their views of politics differ” Catholics left, right and center “all still belong to the same church, one with a vibrant communal tradition and a very well-established hierarchy,” said Green.

Three members of Rhode Island’s congressional delegation are Catholics — all with some Catholic education in their backgrounds. But like their constituents, they are far from being of one accord with the church — or with one another — on issues dear to the church.

Rep. James Langevin’s political profile reflects the complexity of Catholic Rhode Island. He was brought up in the church and is guided in his work, he said, by such Christian admonitions as “Love thy neighbor as thyself.” Langevin has won favor from church-affiliated groups because he is opposed to abortion. But he disappointed some of the same Catholic groups soon after he came to Congress in 2001 when he came out in favor of medical research on stem cells that entails the destruction of human embryos.

Langevin also stressed that “I am more guided by the Constitution” than by Catholic doctrine in his approach to politics. “I represent everyone” in the 2nd Congressional District, he said.

Rep. Patrick J. Kennedy has voted against the procedure that opponents call “partial birth abortion” but otherwise supports abortion rights. Sen. Jack Reed’s backing for abortion rights is politically indistinguishable from the liberal Democratic mainstream. All three men will see the pope at one event or another today and tomorrow.

Green said his research shows that many Catholic voters take into account church teachings that “cut both ways.” Social conservatives, for example, may embrace the church’s condemnation of abortion, but take a harsher view of illegal immigrants than the pope. “There is a weighing process that they feel expected to undertake as people of faith and they make the best choices they can.”

Indeed, America’s Catholic bishops have left an opening for Catholics to exercise just such “prudential judgment” when it comes to choosing among candidates who label themselves “pro-choice” or “pro-life” on the abortion issue.

In their document “Forming Consciences for Faithful Citizenship,” the bishops last fall repeated the church’s view that Catholics are morally bound to seek “full protection for all human life from the moment of conception until natural death.” But the bishops went on to acknowledge there are other policy issues which involve moral judgments as well, such as war, genocide, housing and immigration.

Indeed the bishops said, “There may be times” when a Catholic who opposes a candidate’s position — support for abortion rights, for example — may decide to vote for that candidate for “other morally grave reasons,” though not for mere partisan politics.

A number of religious and political figures have suggested that the diversity of the church’s moral interests make it impossible to pigeonhole Benedict for purposes of U.S. party politics.

Religiously oriented Republican conservatives may take heart from any reinforcement of the church’s well-known positions on what it views as “sanctity of life” issues such as abortion, embryonic stem cell research and euthanasia. But liberal Democrats — not to mention such sometime allies as Mr. Bush and Arizona Sen. John McCain, the GOP presidential candidate — might applaud a full-throated call for better treatment of immigrants.

Providence Bishop Thomas J. Tobin expressed a strong sense that the pope will speak on immigration. Tobin said Benedict may echo the U.S. bishops’ call for “just and effective immigrations laws, which would include the need for secure borders,” the bishop said.

But he said he hopes the pope “will affirm the fact that we have immigrants already here who regardless of their documented status are human beings and children of God, and our brothers and sisters who should be treated with compassion and fairness.”

Whether the pronouncements of the pope will have an effect on this year’s elections is another matter. Green, of the Pew Forum, said the pope could have some indirect impact on the political debate.

For example, Benedict “has been very critical of capitalism, particularly the unregulated variety,” Green said. “If he does that this week, you may find liberals getting very excited” in an environment of economic difficulty.

But Costas Panagopoulos, who heads Fordham University’s political studies, said Benedict’s respect as a world spiritual leader may not translate into a durable effect on a U.S. electorate that does not have a long attention span.

“I don’t think he’ll be overtly political,” said Panagopoulos, “and people know where the pope stands on issues, so he is unlikely to go very far in changing the minds of American voters.”

Whatever the impact, Green, a non-Catholic, said “even liberal Catholics who disagree with him on many issues will feel honored that the pope is coming to the United States, addressing the United Nations.”

Langevin, whose one meeting in Rome with Pope John Paul II in 1998 was “an incredibly moving and powerful experience,” said he was “very excited that the pope is coming.”

rdujardi@projo.com