In the conclusion to their pastoral letter opposing nuclear war, the nation's Roman Catholic bishops insist that they speak as ''pastors, not politicians.'' Debate on this point will certainly continue both within and without the Catholic church. Some have criticized the bishops for involving themselves too intimately with a secular question. They have responded that nuclear war is a moral question and rightly the province of the religious community.
A similar, if less volatile, church-state issue faces the 200-member governing board of the National Council of Churches (NCC), the nation's most influential ecumenical group, as it prepares to meet in San Francisco next week (May 9-13).
The NCC has been under bitter attack from New Right fundamentalists and others for allegedly aiding worldwide revolutionary causes. The flames of controversy have been fanned by reports carried over CBS's ''60 Minutes,'' in the Reader's Digest, and in a booklet issued by the Institute on Religion and Democracy, a Washington-based group with conservative ties.
In public statements, the council, which represents 32 Protestant and Orthodox churches with a reported aggregate membership of 40 million Americans, insists that it has no left-wing bias when it distributes church money abroad or puts its spotlight on human rights violations. Opponents have particularly criticized the NCC for ''misusing'' church funds in supporting a communist government in Vietnam and revolutionary movements in southern Africa.
Next week, council leaders will try to formulate a unified position on this issue as well as other controversial questions facing its various groups. Among the most explosive: whether to accept the membership application of the Universal Fellowship of Metropolitan Community Churches, a new denomination that extends a special appeal to homosexuals.
Spokesmen admit that as the Roman Catholic bishops are not in a position to speak for all Catholic clergy and certainly not all Catholics, so the NCC may have an even tougher task finding consensus among Protestants.
A panel of NCC leaders is expected to make recommendations for restoring unity among member denominations on how to approach secular questions.
Meanwhile, the NCC's president, Bishop James Armstrong, in an impassioned statement this week before the United Methodist Council of Bishops, insisted that ''the National Council of Churches is not a worldwide socialist conspiracy.
''(It) does not supply arms to communists, revolutionaries, or anyone else. The National Council of Churches does not believe in the violent overthrow of any government.''
Bishop Armstrong called media reports about how NCC spends its money ''McCarthy-like'' in nature. (He was referring to the so-called communist witch-hunts of the 1950s, spurred by US Sen. Joseph McCarthy).
However, the NCC president did admit that his group tended to support more left-wing regimes than US-backed right-wing regimes.
''When my government subsidizes the tyranny and trains the military leadership and the police, defends the policies of murderers and torturers while self-righteously condemning the left-wing enemy, I insist it is adding fuel to the flames of international violence - and I have an obligation to speak out,'' the Rev. Mr. Armstrong said.
Not all of the bishop's fellow church officials agree. Some are calling for a detailed account of how NCC money is spent. Fundamentalist groups, including the Rev. Jerry Falwell's Moral Majority, are insisting that Christian clergy turn from humanitarian projects abroad and devote themselves to issues at home, such as prayer in the schools, government aid to parochial institutions, and opposition to abortion on moral and religious grounds.