For Archbishop Raymond G. Hunthausen of Seattle, it's been an upbeat week of pats on the clerical back, friendly episcopal handshakes and blessings of support from his brother Catholic bishops. Two hundred and seventy of them, from powers like Cardinal Terence Cooke of New York, who dined at the White House during the week, to Innocent Hilarion Lotocky of Chicago who ranks 354 in the list of 354 living Catholic prelates, convened here at the annual meeting of the National Conference of Catholic Bishops. It began Monday and concluded Thursday.

Among the rulers in black, Hunthausen, a priest for 35 years who was elevated to the episcopacy in 1962 by Pope John XXIII, was as unlikely a celebrity as he is a leader of what is fast becoming an opposition church.

Last June, in language as forcefully clear as a trumpet blast from Gabriel, Hunthausen looked at the escalating military budget for nuclear weapons and counseled his flock that it was time to cut off the water -- or at least the trickle that each individual controls. He asked the Catholics of Seattle to consider refusing to pay half of their federal income taxes as a protest in conscience against what many in the peace movement see as the nation's war footing: "We have to refuse to give our incense -- in our day, tax dollars -- to the nuclear idol," he said. "Some would call what I am urging 'civil disobedience.' I prefer to see it as obedience to God."

Hunthausen, who has taken to the pavement in public demonstrations at the Trident submarine base in his native Puget Sound area, said last summer that "when crimes are being prepared in our name we must speak plainly." But the plain talk is not expressed in stridence. Hunthausen is a soft-mannered soulful clergyman who looks as if he would prefer hearing confessions at a Little Sisters of the Poor convent to challenging the might of the Pentagon and the Internal Revenue Service.

He knows he is a late arriver on the scene: "My convictions have been with me for a number of years. I just didn't particularly feel comfortable in speaking out." He admits to be edgy about whether he himself will join the growing tax resistance movement: "I have until April 15th, and you can be sure I'm doing some hard thinking."

The lateness and willingness to become vocal, without worrying if men or angels are offended, is a new direction for American Catholicism. More than 50 archbishops and bishops are now members of Pax Christi, the international peace organization. A year ago, less than 20 belonged. A few weeks ago, 29 bishops endorsed a statement of the Intercommunity Center for Peace and Justice that "the possession of nuclear weapons is immoral." In the summer, when Bishop Leroy Matthiesen of Amarillo, Tex., called on workers at a local munitions factory to think about seeking other work, he was quickly supported by the other 11 bishops in the state.

In the corridors and meeting halls of the Capital Hilton, the bishops move and mingle in the amiable good cheer of routine conventioneering. Except for their clerical black and the occasional pectoral cross that a few bishops of the old school hang across their chests, they are little different in demeanor from any other gathering of special interests. A handful wear well-tailored suits, but these are no clotheshorses. A character in the novel "The Vicar of Christ" says of America's Roman Catholic prelates: "Most of them are peasants, my dear chap, but a single generation removed from the affluence pumped onto our shores from the bilges of the immigrant ships." The bishops wouldn't argue with that. Some would say, proudly, that they were appointed to their jobs by the peasant John XXIII.

A sanctuary could be filled with the questions raised this week.

Is this a revolutionary moment for the bishops or are they merely a slow-moving patriarchal group lurching to a position they might have taken long ago? Is the American Catholic church becoming a peace church, or are a few of its leaders catching up to Pope Paul VI's 1965 cry of "No more war; never war again"? Or are they losing touch with the Catholics who want bishops as administrative leaders only? And in its moral opposition to the nuclear arms buildup, how much of the church's episcopal power can be transferred into effective political power?

History isn't moving so fast that the events of only 15 years ago aren't instructive. In "American Catholics," a new book by James Hennesey, a Jesuit and professor of religious history at Boston College, the bishops' record in the Vietnam war is detailed.

"The Catholic bishops had in 1966 reached a hesitant judgment that, on balance, American involvement in Vietnam was justified," Hennesey writes. "Two years later, in the wide-ranging pastoral letter 'Human Life in Our Day,' they were less sure. Defending the 'fundamental right of political dissent,' and advocating 'rational debate' on public policy, the letter tried to apply traditional 'just war' criteria to the situation. The 'inhuman dimension of suffering' and the physical losses being sustained in Vietnam were weighed against prospective 'disastrous' effects of 'untimely withdrawal.' "

If the historical record is there, so are some current sentiments from within the church. The opposition church has opposition itself. Paul Weyrich, an Eastern Rite Roman Catholic and the head of the Committee for the Survival of a Free Congress, states that he has "no quarrel with those bishops who say there are great moral issues involved in war and peace. But I just don't think that many of them are informed at all on the strategic nuclear situation in which we find ourselves . . . If you've ever met a Catholic bishop -- and I have met many of them -- and attempted to hold a reasonable conversation with them on political issues, you find out how truly ignorant they are -- not just on this question but a whole variety of them."

Weyrich, who calls Hunthausen "a radical of longstanding," believes that the peace bishops "are taking themselves further and further away from their Catholic constituency . . . The people aren't going to take them seriously."

When Hunthausen was asked whether his thinking has seeped into the parishes of his Seattle archdiocese, he replied that the answer is not yet in: "I have some indication both ways. There have been people who have responded positively. They feel that the church is now more relevant in their lives. But there have also been people who have been frightened by it. People feel that this is not the role of the bishop."