President Reagan's decision to establish full diplomatic ties with the Vatican is seen here as part of a step-by-step effort to win critical Roman Catholic support in the 1984 election.
But beyond the politics of the issue there lie deeply rooted constitutional, historical, and denominational concerns.
As for politics, Mr. Reagan's earlier backing of tuition tax credits for students in private and parochial schools was a bid for middle-class Catholic voters who have long lobbied for such federal assistance.
Full ties with the Vatican should help the President with a another group that has frequently nettled the White House - the leadership of the Roman Catholic Church in the United States.
Sending an ambassador to the Vatican has some risks. It could stir up American Protestants and result in embarrassing confrontations in Congress in coming months. But the consensus here - at least among a wide range of political experts - is that the President will probably come away from this decision unscathed.
That means Reagan could pick up some important political points.
''While the average Catholic probably doesn't care much, if at all, about this issue, there is one group of Catholics who care very, very, very much. That is the church leadership in this country. This is a burning issue with them,'' one Republican insider notes.
This is the same group of church leaders which has irritated the President on issues such as the nuclear freeze and modernization of atomic weapons, and on sensitive problems such as the poor and hunger in America.
''It's hard for a President to discredit something like the freeze movement when a group like the (National Conference of) Catholic Bishops are on that team ,'' notes Dr. Norman Ornstein, a political analyst at the American Enterprise Institute. ''But if a move like this can blunt their outspokenness, it helps the President.''
A leading Republican observes that a move like this can soften criticism of the President from Catholic pulpits in this election year, and deflect what might otherwise be sharp criticism of other policies in many newspapers published by the Catholic Church.
All of this, however, depends on the Vatican issue's quickly fading from public view. Otherwise, there could be a Protestant backlash that could be particularly costly to the President in the South.
But the issue may not fade. Dr. James M. Dunn of the Baptist Joint Committee on Public Affairs indicated Wednesday that he may support efforts to block establishment of relations with the Vatican in both Congress and the courts.
Americans United for Separation of Church and State has indicated that a suit will be filed on First Amendment grounds attempting to abrogate formal ties with the papal ministate. Others, such as Dr. Dunn, say they will also begin to apply pressure on Congress to reject confirmation of William A. Wilson, the President's choice as the ambassador to the Vatican.
Sen. Ernest F. Hollings (D) of South Carolina, the ranking minority member of the Senate Appropriations subcommittee, said that he would fight the approval of funds to establish the US mission at the Vatican.
In all of this, it is important to note that among Protestants there is almost none of the hysteria, fear, and even hatred that marked the anti-Catholic movements that swept the US in the 19th and early 20th centuries.
Comments from Protestant leaders have been firm, but restrained. Objections are voiced on constitutional grounds. Various Protestant leaders say they would object to the US sending an ambassador to represent the country at the headquarters of any religion, Catholic or otherwise.
Objections have come from a number of groups, both liberal and conservative, including the National Council of Churches, the Baptist Joint Committee, and the National Association of Evangelicals. Also protesting has been the American Jewish Congress.
Gordon Engen, an official with the Seventh-day Adventists in Washington, says there is a ''surge of concern'' about Reagan's decision. But this concern is far different than in earlier years, when there was ''fear'' among Protestants of Roman Catholic political power.
''These fears have been allayed today by the fact that there was a Catholic president, John F. Kennedy,'' says Mr. Engen. ''Today there is not an anti-Catholic climate in this protest. But today we say that if the US government was going to establish relations with any church, there would be protest.''
The reason is that the American constitutional experience is quite different from that in the other 100-plus nations that have already sent ambassadors to the Vatican, Engen says.
In the US, it was recognized that religious freedom is a God-given right, rather than something a government grants to the people. In that way, the US approaches church-state relations differently. The Constitution states that this is a God-given freedom, and then tells Congress, in the First Amendment, to keep its hands off this freedom.
The argument goes that if churches start getting involved with government, as some politicians urge with such issues as prayer in the public schools, tuition tax credits, and now formal ties with the Vatican, then it opens the door to trouble. Eventually, this could open the way for government to get involved in church matters.
The great advantage of avoiding such intermingling has been that it allows people of many faiths to live side by side in harmony.
Mark Russell of the National Conference of Catholic Bishops says the doctrine of separation of church and state is one upon which honest people can differ. This is the case, he says, so far as the Protestant leadership and the Catholic Bishops are concerned on the issue of Vatican relations.
Mr. Russell says says the US already has relations with Israel, which he says might be considered a religious state, and with some Islamic countries where religion is supreme. In the Vatican, the Pope heads both the church and the temporal government, where he is the head of state.
From the viewpoint of Election '84, the Catholic vote presents a tremendous temptation to any politician. For Republicans, there are two principal targets: the Sunbelt, with its mostly Catholic Hispanic bloc, and the Industrial Belt, with blue-collar Catholic ethnic groups and a growing number of upwardly mobile white-collar, middle-class Catholics.