The nation's mainline Protestant and Roman Catholic churches, largely silent about U.S. military intervention in Vietnam until late in the conflict, have become centers of opposition to the war against Iraq and important participants in the anti-war movement.

The early and vocal criticism of President Bush's gulf policies from the National Council of Churches and the National Conference of Catholic Bishops marks a historic shift in the public attitudes of the Christian churches toward the issues of war and peace and a sharp change in how the national churches see their relationship to governmental authorities.

The shift is expected to be dramatized in today's anti-war demonstrations by the presence of substantial church contingents.

Few see the contrast with the early days of the Vietnam War more clearly than Richard John Neuhaus, director of the Institute on Religion and Public Life, a research institute based in New York City. Along with the Rev. Daniel Berrigan and the late Rabbi Abraham Heschel, Neuhaus formed a small anti-war group in 1964 called Clergy and Laity Concerned About Vietnam.

"At that time, there was a perception that what we were doing was a daring thing to do," Neuhaus recalled. "Today, what was then deemed the normal thing would require considerable daring, that is, to say that military intervention in the gulf is a reasoned moral policy."

Neuhaus supports U.S. policy this time, and that puts him at odds with much of the Catholic and mainline Protestant leadership, which began expressing strong reservations about the president's policies in November.

Since then, organizational efforts have mushroomed. The churches demonstrated opposition even before the war started. A Jan. 14 march from the Washington Cathedral to the White House drew more than 5,000 people -- including the president's own bishop, the Most Rev. Edmond L. Browning of the Episcopal Church; the Rev. Joan Brown Campbell, the incoming general secretary of the National Council of Churches, and the heads of all major black Protestant bodies.

Not all major church figures oppose the war. For example, Cardinal Bernard Law, the Roman Catholic Archbishop of Boston, said last week that prayers for peace are "not fulfilled at the price of granting tyrants and aggressors an open field to achieve unjust ends."

The leaders of evangelical and fundamentalist churches have, for the most part, been absent from the anti-war protests -- though they have also been notably restrained in support. And it is by no means clear that the church leaders who oppose the war necessarily reflect the views of their members. Polls show strong support so far for Bush's actions.

The new anti-war activism clearly represents a break from the patterns of church behavior established after World War II, when mainline Protestant and Catholic leaders generally played down political issues and devoted their energies to internal church issues such as the boom in church membership. In that period, many Protestant and Catholic leaders were influenced by the theology of Reinhold Niebuhr, whose support for "realism" in foreign policy won a wide hearing.

Moreover, many Christians -- especially Roman Catholics -- strongly identified with the anti-communism that was at the core of post-war U.S. foreign policy. This won presidents and the military important support from such key religious leaders as New York's Cardinal Francis Spellman and such popular Protestant leaders as Billy Graham and Norman Vincent Peale.

But the Vietnam War had at least as dramatic an effect on church leaders as it had on the rest of society, reviving the Christian anti-war tradition, strengthening existing pacifist organizations, and spawning new ones.

One of the most successful of the new organizations was the Washington-based Sojourners, which publishes a magazine that combines a strong emphasis on scripture with a radical political vision.

Founder Jim Wallis recalls being pushed out of his home church in Detroit in the 1960s because of his participation in civil rights and anti-war protests. By 1975, as a student at Michigan State University, he still "didn't see many Christians involved in social causes."

Wallis, an evangelical Christian, and six friends at Michigan State started Sojourners that year with contributions of $100 each from their next semester's tuition. The magazine took off, fitting neatly with the movement toward the left within the mainline Protestant leadership.

Christian groups played central parts in the nuclear freeze movement, and in the battles against the Reagan administration's Central American policies and apartheid in South Africa. "When the gulf crisis hit, you had these personal relationships {among Christian organizations} that weren't there before," Wallis said.

The progressive Protestant leaders explained their political agenda by referring to traditional Christian concepts of justice, equity and brotherhood and argued that U.S. foreign policy abetted the privileged at the expense of the poor. In the meantime, the country's Catholic bishops issued pastoral letters on nuclear arms and the economy, both of which had a strongly liberal cast.

Critics of both the National Council of Churches (NCC) and the Catholic Bishops, such as George Weigel, president of the Ethics and Public Policy Center, charge that the new religious ideology is based on simplistic economics and a reflexive opposition to the use of American power -- reflected again in the war with Iraq.

"The NCC was immeasurably more concerned about the possibility of the use of U.S. military force in the Persian Gulf than it was about resisting the aggression of Saddam Hussein," Weigel said. He added that the religious left so wanted to cling to the Vietnam legacy that its opposition to war in the gulf is "grounded not in a concern that American military action would fail but in a deep fear that it would succeed."

Once the war began, some religious leaders softened their stance. While a handful of Catholic bishops renewed their opposition, the Bishops' Conference has moved to emphasizing the need to fight in accord with "just war" principles by minimizing civilian casualties and limiting the duration of the conflict.

The Rev. J. Bryan Hehir, a professor of ethics at Georgetown University and one of the principal architects of the nuclear pastoral, said that the reticence of some bishops reflects the moral ambiguities of the conflict.

But Catholic peace groups, notably Pax Christi and many of the women's religious orders, remain mobilized to fight the war, as is most of the mainline Protestant leadership.

Wallis said he hopes the large presence of church groups in the current anti-war movement will make it more appealing to the mainstream than movements dominated by the secular left. He added that while today's demonstrations were largely organized by left-of-center political organizations, the church groups will demand a larger role as the movement develops.

"We will not be an appendage to a movement run by the left," Wallis said. "We're either going to work together -- with the churches playing a leadership role -- or we'll organize ourselves and bring the mainstream with us."