MICHAEL NOVAK pauses for a moment of mild self-congratulation. Conservatism's most prolific and often most biting critic of U.S. Catholic bishops says that "in the big things," last week's final pastoral letter on war and peace "is very much like my own view. The final draft has made all the basic changes that were most important to me."

At this point, a check of the score sheets--Novak's and other judges'--is necessary. Such pacifist bishops as Walter Sullivan of Richmond and Thomas Gumbleton of Detroit, men Novak had in mind last year when he derided "the new extremists" in the church's peace leadership, are also pleased with the letter.

So is the liberal National Catholic Reporter. Its editor, Thomas Fox, applauds the document as a basic diversion from the nuclear policies supported by the Reagan administration and conservatives like Novak. "It's understandable," said Fox yesterday, "that the right wants to put the best possible face on an ugly situation from their perspective." Fox is "skeptical that deep down in Novak's heart he finds the letter a positive development."

Where lies the heart of Novak is one of the sub-mysteries of current church politics. The enigma grows larger when placed in the context of a many-sided career marked by frequent job changes and unpredictable shifts of thought and allegiances. An author (17 books) and a lecturer (about 30 speeches a year), Novak reached a new prominence last month when the entire April 1 issue of the National Review, where Novak is religion editor, was devoted to a reprint of Novak's open letter to the Catholic bishops. Introducing the piece, "Moral Clarity in the Nuclear Age," the magazine's editor, William F. Buckley Jr., hailed it as "a document for the age."

Novak, who displays a photograph of himself with Pope John Paul II in his American Enterprise Institute office, says half-jokingly that of late he has been feeling like a pope: lecturing bishops on what to think. In the Novak papacy, 12 encyclicals, ranging from "Born Again Bishops" in the National Review to "Arms and the Church" in Commentary, were issued in 1982 alone. In apocalyptic tones, he wrote in The Wall Street Journal that an "era of divisiveness" was being created by some of the bishops. "Men and women of conscience will have to resist them with every force of intellect they possess. For the good name of Catholicism is also at stake, together with liberty of conscience everywhere."

Whether seen as expressions of careful insight from a loyal son of the church or as ranting screeds from a Catholic Falwell, the Novak texts were part of the pressure that led to a softening of the bishops' letter as it was rewritten from the second draft to the third. Novak, who said the second draft "moves the world very close to war," acknowledges that the return to the word "halt," as opposed to "curb," which was in the third draft and referred to the building and use of nuclear weapons, was a change he didn't like. But that change, hailed by liberals as a major victory, was to Novak merely "symbolic."

He says he was heartened that the bishops "explicitly turn aside from the notion of condemning deterrence." He supports the bishops' clear distinction between pacifism as a personal option and a public option for nations. And the bishops "protect the role of the laity in prudential matters and judgments of circumstance . . . That, to me, is the number one issue . . . The bishops were in earlier drafts inflating some of their prudential judgments with bishops' authority. They don't do that now."

Starting in January Novak regularly dispatched drafts of his own letter to the bishops' committee. Those drafts put Novak out front as the leading critic of the bishops.

He was a sought-after voice. Last month, Rep. Vin Weber, a second-term Republican conservative from Minnesota, invited Novak to lecture a group of 30 Catholic senators and House members on the bishops' letter. "I think he's the leading neoconservative Catholic intellectual," said Weber, a friend. "I was very pleased with the meeting. We plan to bring him back to the Hill again."

In his 12th-floor corner office--with gold-hued curtains that shape a view over the buildingscape of downtown Washington--Novak reaches to a table behind his chair where there is a small stack of his "document for the age." It is a few days before the Chicago meeting of the bishops. "It's gotten a tremendous response," he says, offering a copy, along with a sheaf of other previous articles. One wall is dominated by large lithographs of the Four Horsemen of the Apocalypse. They are by Karen Laub-Novak, Novak's wife of 19 years and a nationally recognized artist and illustrator.

Since 1960, Novak, 49, has been a teacher (Stanford, State University of New York at Stony Brook, Syracuse), a political speech writer, a Rockefeller Foundation official, a Reagan appointee as chief of the U.S. delegation to the U.N. Human Rights Commission meeting in Geneva and a columnist. About the last, Novak says he "almost won" the Pulitzer Prize--in 1979. He dropped the column, which ran in about 30 newspapers, in 1980. For the past five years he has been a "resident scholar" at the American Enterprise Institute, coming to the conservative think tank from Syracuse University. He and his wife, with a son and two daughters, moved to the Chevy Chase section of Northwest Washington in 1978.

Novak's ease with the nuances of ecclesiastical thought is not a coincidence. As a seminarian studying for 12 years in the Congregation of the Holy Cross (the order that runs Notre Dame University), Novak spent two years at the Gregorian university in Rome. He joined the order in 1947 as a 14-year-old eighth-grader from a Catholic family in Johnstown, Pa. Novak left the order leaving before ordination. In early 1960, he was dispensed from his Holy Cross vows.

From then until 1965, Novak was a graduate student at Harvard. He earned a master's, but not a PhD. He became a follower of Reinhold Niebuhr. Among other magazines, he wrote for Commonweal, the liberal weekly. With his wife, an Iowan whose father was a liberal Democrat and twice ran unsuccessfully for Congress against the late Rep. H.R. Gross, Novak returned to Rome. That was the year Vatican II began. Novak wrote a well-received book on it, "The Open Church." In 1967, with a growing reputation as a rising-star liberal Catholic, he accepted a teaching job in the new Department of Religion at Stanford University. The campus anti-Vietnam War fervor was peaking and Novak, sympathetic to the protests of student radicals, added his voice to the antiwar left. That summer he went to Vietnam as a journalist. He favored a gradual withdrawal of U.S. forces, that Vietnam's future should be left to the Vietnamese. He wrote that "the legacy of destruction Americans are leaving in Vietnam will not make our children proud."

By the late '60s, Novak had moved further left. He had written "A Theology for Radical Politics" and "A Time to Build," a collection of essays. In one of them, "American Catholicism After the Council," Novak inveighed against American bishops for their conservatism. This was during the period when the bishops supported the Vietnam War and were opponents of anything tainted with communism. For Novak, "the dirty word" for many of the American bishops was "secularism." "They blame on it virtually every ill that plagues society, from racial discrimination to lurid advertising. The bishops hardly ever recognize their own complicity in the evils of modern life; one seldom hears them, as a group, confess their own sins. There are, after all, bishops who have in the name of prudence compromised their professed moral code in the matter of race (but who in the name of the same prudence brook no compromise in the matter of birth control). But most of all, the bishops have yet to come to grips with the fact that atheism and agnosticism represent a noble way of life."

What happened? How did a man move from ridiculing the bishops for too much prudence in 1967 to blasting them for having too little 15 years later? In 1968, Novak, from the far left, urged antiwar Democrats not to rally behind Hubert Humphrey. True, he said, that might throw the election to Richard Nixon, but a Nixon presidency would help the Democrats' effort "to rebuild the party for 1972." As one of the would-be rebuilders, Novak joined the McGovern campaign. Among other things, he wrote speeches and position papers.

Eight years later, Novak was an ardent Reaganite. In a 1980 Commonweal article on "Why I Am Voting for Reagan," Novak expressed, first, his contempt for Jimmy Carter: "He is a dirty, mean campaigner." In Reagan, whom Novak had opposed while at Stanford during Reagan's first gubernatorial election, there was now the appeal of "implacable affability." Reagan is "a builder, not a knocker . . . On his feet he thinks as quickly as, and with greater common sense, clarity and humor than, the two pietists Carter and John Anderson with whom he is competing for our votes. He has faced heavy weather from the more sophisticated parts of our population. This, too, endears him to me."

Other shifts and lurchings, though less dramatic than radicalism to Reaganism, occurred. In a 1971 book, "Ascent of the Mountain, Flight of the Dove," Novak wrote as though he were a disciple of Ralph Nader: "Modern corporations are not merely instruments to which one gives a part of one's life. They tend to be all-absorbing not through totalistic dedication but through dividing one's personal autonomy from one's corporate role. They divide one's creativity, imagination, feelings, and hopes from one's performance for the company." At AEI, which receives funds from more than 600 corporations, one of Novak's recent efforts was a booklet called "A Theology of the Corporation." He discussed seven ways that "corporations offer metaphors for grace, a kind of insight into God's ways in history."

Another shift involved Novak's acceptance of white Anglo-Saxon Protestants, a group whose cultural values he once disdained. In his 1971 book, "The Rise of the Unmeltable Ethnics," a work that celebrated the author's Slovak ancestry, Novak ridiculed the "sickness" of WASP society: "The WASP way . . . is to put a harsh rein upon the impulses of man's animal nature, to place him in the halter of the industrial machine, and to order him docilely to produce."

The one-time stinger of WASPs now sends his two daughters to the WASP elite National Cathedral School for Girls.

Novak sees intellectual development, not inconsistency, in these changes. He takes pride in portraying himself as the older and wiser observer who, about to turn 50 and seasoned by surviving the battles, has come to the maturity of being able to look back reflectively.

"The world has changed a great deal," he said, leaning over his desk and speaking in a low voice. "I've always argued that you should question your own positions. When I've seen things not work the way I thought they would work, I've adjusted accordingly. I was opposed to the war in Vietnam and said so out of concern for what was happening to the Vietnamese. When I see what's happened to the Vietnamese since we've abandoned them, I question a good many of my judgments about the war. After I see the information which keeps coming out from the Vietnamese side, some of the factual judgments on which I based my opposition turned out to be wrong."

As part of the religious right and calling himself a "neoliberal," Novak acknowledges that he no longer feels "quite at home" in liberal publications like Commonweal and The National Catholic Reporter. In his new book "Confessions of a Catholic," to be published in June, Novak strikes his breast at his celebrations 20 years ago of an open church. "What the barbarian invasions, centuries of primitive village life, medieval plagues and disease, wars, revolutions, heresies and schisms had failed to do, the Second Vatican Council succeeded in doing. It set in motion both positive forces and forces that squandered the inheritance of the church . . . I have seen many individual lives ravaged by novel interpretations in faith and morals . . . But the new libertinism seems less the result of human frailty than of the ideology of 'openness' and 'liberation.' "

From the left, few cheeks have been turning to receive Novak's slaps. Last month in The National Catholic Reporter, columnist Tom Blackburn wrote that "ever since Michael Novak announced his neo-Niehbuhr phase (subtitled 'How I Learned to Stop Worrying and Love the Bomb'), he has organized magazines and manifestos faster than Mickey Rooney could say, 'I know! Let's put on a show!' " Another National Catholic columnist, Arthur Jones, wrote last month that "Michael Novak preaches capitalism's virtues to Christians. The breakthrough will come when he simultaneously preaches Christian virtues to his capitalist backers."

In Washington, one of Novak's liberal critics is the Rev. Msgr. Geno Baroni. He goes back with Novak many years, not only to the early 1970s when they were aligned in creating a stronger identity for ethnics but also to the Johnstown, Pa., area where the Novak and Baroni families lived. "I like him as a person," Baroni said last week. "I taught one of his brothers in high school. It was the great American story--the immigrant family educating their kids. Here's Michael, a Catholic kid, going to Harvard and Stanford. The question a lot of us have now is that he has moved from one kind of tradition to another. To him, that's very logical, but to us it makes us constantly surprised where he's ended up. And where he will end up."

Novak sees himself as a searcher among ideas. "I am not where I was a decade ago," he writes in "Confessions of a Catholic," "just as then I was beyond where I had been a decade before that. Such a record necessarily mirrors a pilgrim's progress." He is aware of his "many and vocal critics." They "do not fault me for theological deviation; they fault me for breaking ranks on politics . . . Some care not whether you question, probe, explore, create--their litmus test is heartfelt verbal repetition."

The opinions of friends and critics aside, one Novak trait that came across in three interviews is a love of attention bordering on vanity. He quotes what Time magazine wrote about him. He recounts some banter with the pope: John Paul II had noticed Novak's Solidarity button but not "my Adam Smith tie." He refers to his near-Pulitzer. He passes out unrequested articles about himself.

Novak dismisses much of the criticism against him as "ad hominem." Many on the left, he says, are "intellectually dishonest." Others, he has written, "are lazy. The left establishes its moral and religious vision not by argument but by declamation. And it seldom counts the costs of its institutional reforms, never with the same mental ferocity it applies to institutions it opposes."

With his newest friends, Novak is popular, respected and well-liked. In a December 1981 speech, Vice President George Bush quoted a "brilliant paper" of Novak's. Later in the speech, Bush alluded to a Novak thought that "I found fascinating." In February, a bishop to whom Novak had sent a draft of his letter to the hierarchy wrote back with hearty thanks.

The bishop was so impressed with the text that he offered to send a donation to help cover the costs of the mailing.