Through most of this nation's history, the Roman Catholic Church could be counted on to bless without reservation almost any military venture the country embarked on. But a movement developing in the highest levels of the church within the past year is changing that.

During the year, more than 40 of the church's bishops, from New Ulm to Nashville, from Peoria to Paterson, have individually and on their own initiative issued public statements criticizing this nation's nuclear arms policy. Their actions have stirred controversy, both in the church and outside it, but far from being discouraged by that, their numbers seem to be growing.

Last month, Archbishop John Roach of St. Paul-Minneapolis, president of the nation's Catholic hierarchy, in his state-of-the-church address called the nuclear arms race "the most dangerous moral issue in the public order today." The church, Roach declared, "needs to say 'no' clearly and decisively to the use of nuclear weapons."

In October, Roach's immediate predecessor as president of the National Conference of Catholic Bishops, Archbishop John Quinn of San Francisco, marked the 800th anniversary celebration of his city's patron saint with a statement proclaiming: "The teaching of the church is clear: nuclear weapons and the arms race must be condemned as immoral."

Quinn urged the Catholic hospitals within his jurisdiction to refuse to cooperate with military contingency planning in the event of a nuclear attack, because such planning only fosters "the illusion that there can be an effective medical response" to a nuclear war.

Earlier in the summer, Amarillo Bishop Leroy Matthiesen, whose diocese includes the Pantex plant where nuclear warheads are assembled, told his people that nuclear weapons are immoral and suggested that those who worked at Pantex should quit and find other jobs. Twelve other Texas bishops subsequently endorsed his stand.

In June, Archbishop Raymond Hunthausen of Seattle denounced nuclear weaponry, called for unilateral disarmament by the United States if necessary to deescalate the arms race, and suggested that Christians consider withholding part of their taxes to protest the arms buildup.

The impact of the individual bishops' statements has been buttressed by repeated statements by Pope John Paul II, pleading with world leaders for deescalation of the nuclear arms race and a greater commitment to disarmament negotiations.

Last week, this message was delivered personally in extraordinary visits to the White House by a delegation of American scientists who are members of the Vatican's 400 year-old Pontifical Academy of Sciences. Similar visits, also pleading for worldwide reduction in nuclear arms, were scheduled with world leaders in Moscow, Paris and London.

The pontiff will make his appeal once again in his World Day of Peace message, to be read New Year's Day. "Given the destructive capacity of present day military stockpiles," he says, "it is the survival of the whole human race that is at stake."

The upsurge of criticism by the bishops is linked to dissatisfaction with the nuclear policies of the Reagan administration.

"A collision between Catholic moral teaching and U.S. nuclear policy . . . has been a probability ever since the end of last year when not only was SALT II rejected but the Reagan administration began installing in office many of the treaty's most devoted foes and began giving a warm hearing to theories of 'fighting' and 'winning' nuclear wars," says an editorial in the current issue of Commonweal, an unofficial Catholic journal.

Nowhere is the church's changed attitude toward war and patriotism more dramatically illustrated than in New York City, where only a little more than a dozen years ago, Cardinal Francis J. Spellman responded to criticism of the United States' military involvement in Vietnam with "My country right or wrong -- my country." Only a handful of antiwar activists in the church registered outrage over that attitude at the time.

Today, Spellman's hand-picked successor, Cardinal Terence Cooke, is under fire from priests, nuns and lay members for a letter he wrote to chaplains in which he called for nuclear deescalation but said that "a strategy of nuclear deterrence can be morally tolerated if a nation is sincerely trying to come up with a rational alternative."

Two days after Cooke's letter to the chaplains was made public, groups of clergy, nuns and lay persons -- including some officials of the archdiocese -- accused the cardinal of providing the theological rationale for the Reagan administration's increased military spending and nuclear policy.

A similar controversy broke out earlier this month in Norfolk, which is heavily Navy-oriented. Speaking in a church there, Bishop John J. O'Connor, a former Navy chaplain and now auxiliary to Cooke in the Military Vicariate -- the ministry to Catholics in the armed forces -- took sharp issue with the local Bishop Walter Sullivan, one of the most peace-oriented members of the hierarchy.

In October, Sullivan had declared that it is "immoral to be associated with the production or use of nuclear weapons" and that nuclear bombs are "absolutely incompatible" with the Gospel of Jesus Christ.

O'Connor disagreed. "I know of nothing in official church teaching that suggests that our military people are engaged in immoral activity in carrying out their military responsibilities," even if their duties involve nuclear weaponry, he said.

Two days later, the diocesan priests' council weighed into the debate with its own statement, coming down unanimously on the side of Sullivan. "The teaching of the church is clear; nuclear war and the arms race are immoral," it said.

The American bishops are midway through a detailed two-year study of war and peace, which is expected to produce a formal position next year on the morality of modern warfare. The interim report on the study, given to the bishops last month by Archbishop Joseph L. Bernardin, seemed to offer some clues to the direction the final report may take.

As moral teachers, he said, "We need to be convinced that some actions can never be taken, even for survival; that there are limits to the argument that, because our adversaries are considering something, we must be prepared to do it also . . . The very created order is threatened by nuclear war . . . ."

Bishop Thomas C. Kelly, general secretary of the Bishops' Conference, said the response from Catholics across the nation to this report as well as Roach's denunciation of nuclear warfare "has been excellent . . . We've heard from very respectable groups that I would not expect to hear from very frequently." Most, he said, agreed with the bishops

Given the independent mood of Catholics today, it is hard to predict how much influence the bishops' leadership will have on the nation's 50 million Catholics on the nuclear issue. Every sociological study for the last decade has shown that on birth control, for instance, relatively few Catholics still look to the church for moral guidance. But on abortion, the hierarchy has pretty well held the line, and a powerful lobby has emerged to support the church's viewpoint.

Catholic author Msgr. Vincent A. Yzermans, a veteran observer of the church, believes that the church's present wrestling with the nuclear issue will be more like its battle with abortion than with contraception.

Writing in The New York Times last month he said: "Something is stirring in the Roman Catholic Church that portends an explosion between church and state that will make the abortion issue, the school-aid controversy, and the tax-exempt status of churches look like a child's sparkler on the Fourth of July."

The Catholic Church's involvement with the peace issue, he predicted, presages "the most significant revolution within the American Catholic Church since Lord Baltimore's contingent of Catholics disembarked on Maryland's shores in 1634."