For more than a year, Sen. David F. Durenberger (R-Minn.) has been passing through what he and his friends describe as a sometimes painful personal transition, a kind of midlife crisis. Characteristically, Durenberger's tribulations have been a little unconventional -- they have proceeded in public view in his home state at the same time he has regularly made headlines here as the outspoken chairman of the Select Committee on Intelligence.

Thirteen months ago, Durenberger and his wife, Penny, separated after years of a troubled marriage. The separation was announced by Durenberger's office. At the age of 51, despite continuing success in his career as a public official, Durenberger found himself a deeply unhappy man. He moved out of the family house in McLean and into the Cedars, a nondenominational Christian retreat house in Arlington overlooking the Potomac River.

There, he said in a recent interview, he has been making "sort of a historical review of some of the events in my life and how I was unhappy in my relationship with my wife and with other people."

Durenberger's willingness to speak publicly about his private agonies -- which he first did last fall to Steve Berg, a Washington reporter for The Minneapolis Star and Tribune -- is one example of an unusual political personality. Another example is his willingness to speak his mind, sometimes bluntly, as chairman of what is considered one of the most sensitive committees in Congress.

Since taking over the chairmanship of the intelligence committee in January 1985, Durenberger has publicly feuded with CIA Director William J. Casey, most recently suggesting that the nation's top intelligence agency lacked "a sense of direction" under Casey's leadership. Last fall, Durenberger won his committee's approval for the release of a highly critical committee report on the Philippine government of then-President Ferdinand Marcos, and he followed this up at a news conference at which he called for Marcos' resignation.

Durenberger is described by the committee's senior Democrat, Sen. Patrick J. Leahy (Vt.), as "aggressive" and a "forceful character." In reorganizing the committee's staff in an attempt to make it more professional, he "ruffled some feathers along the way," said Sen. David L. Boren (D-Okla.), another committee member. Committed to an active and as public as possible intelligence oversight role for Congress, Durenberger has strong opinions and is not timid about voicing them.

He came to the chairmanship with an agenda, at the top of which was the creation of a "national intelligence strategy." Too often, he believed, the congressional oversight role has been to "shoot the wounded" -- delving into intelligence operations after the fact -- rather than as a mechanism to shape national intelligence goals.

Durenberger's criticism of the Central Intelligence Agency for lacking "a sense of direction" was part of this approach, which was bound to bring him into conflict with professionals in the intelligence community.

Despite Durenberger's friction with him, Casey delivered the first such national intelligence strategy to the committee this month, according to Durenberger.

Durenberger's tenure as committee chairman, which ends with the conclusion of the 99th Congress later this year, has been made all the more controversial by developments in the intelligence community. Last year was the "year of the spy," marked by the redefection to the Soviet Union of KGB agent Vitaly Yurchenko and several highly publicized cases of alleged espionage by agents for Israel, China and the Soviet Union.

Combined with this was the controversy over leaks of sensitive intelligence information, which was highlighted by the disclosure in The Washington Post last Nov. 3 of a CIA plan to help Libya's neighbors or opponents to topple the regime of Col. Muammar Qaddafi.

This prompted an unusual private meeting last fall between members of Durenberger's committee and members of the House Permanent Select Committee on Intelligence, which the House members requested.

While most intelligence leaks may come from the executive branch, a House source said, the seeming turmoil in the intelligence community "when combined with guys like Durenberger and others speaking out" alarmed some House members.

"Members were concerned that they would get swiped with the same brush," the source said.

This House attitude -- and that of many of Durenberger's critics -- was voiced about the same time by Rep. Edward P. Boland (D-Mass.), known in the House as "Mr. Intelligence" for his earlier service as chairman of the House committee.

Without mentioning Durenberger by name, Boland rose on the House floor Nov. 19, a few days after an acrimonious public exchange in which Casey, responding to Durenberger's criticism of the CIA, accused the Senate committee of conducting its oversight function in an "off-the-cuff" manner that resulted in the "repeated compromise of sensitive intelligence sources and methods."

As chairman of the House committee, Boland said, "I did not find it necessary to proclaim publicly every disagreement with the intelligence agencies . . . . I do not believe that it is helpful or appropriate for members of Congress who sit on oversight committees to regularly or recklessly comment on intelligence matters, either critically or favorably."

These swirling controversies of last fall appeared to be vintage Durenberger, fitting in perfectly with his public image as an independent politician who was not afraid to speak his mind. It was an image of a hard driving, some would say driven, man who was, in his own words, "out to change the world."

Yet, at the same time, according to Durenberger, he was in private becoming a changed man, one who looked back on a life of public triumphs and found that they had masked, even from himself, private failures.

Before his election to a second term in 1982, Durenberger rarely took the time to look back on anything. He had been planning to run for governor in 1978, but found himself his party's choice that year in the race to complete the term of the late Sen. Hubert H. Humphrey (D-Minn.). Unexpectedly, Durenberger won.

He threw himself into his job as a senator with a vengeance. Described by Thomas Horner, his former administrative assistant, as "a workaholic" with "an enormous need and desire to succeed," Durenberger viewed his truncated, four-year first term as perhaps his only chance to have an impact on the public policy issues that so concerned him. There was so much he wanted to do, and possibly so little time.

In 1982, Durenberger won his own six-year term, leading the GOP ticket after a grueling campaign against Democrat Mark Dayton, a department store heir who poured $7 million of his own money into the contest. Durenberger had more time now for his public pursuits, yet it was after this, according to Horner and others, that he began privately to question where he was headed.

"Dave did approach a midlife crisis -- a lot of things came together in his life that caused him to step back and look at where he wanted to go," Horner said. "I think he had a hard time dealing with what it was he worked so hard to achieve."

Durenberger said of this period:

"I relaxed for the first time then. I didn't have to prove anything to anybody." But he did have to ask himself, "Now what?" and to contemplate six more years of the same type of frenzied, driven life style as he sought to shape public policy on such issues as health care according to his vision.

"Is that the most important thing you want out of your life?" Durenberger recalled asking himself. "Well, it's the most important part of your job. But is your job the most important thing in your life?

"At that point I started looking at the relationships with the kids, with Penny, with my colleagues and friends. Those things are a hell of a lot more important than being a recently reelected senator. And I wasn't happy."

At the peak of his public success, Durenberger's private life in the early 1980s was in shambles. Two of his four sons had drug problems. Durenberger's first wife, Judy, died of cancer in 1970, and Penny had taken on the burden of rearing Durenberger's children while Durenberger pursued his career. Their marriage was not a happy one.

In January, they separated, by which time Durenberger knew he needed help in coming to terms with his shattered private life, his image of himself as "a bad person." He accepted an offer from Doug Coe, whom he knew through the Senate Prayer Breakfast organization, for a place at the Cedars, which Coe and others operate as a guest house.

Coe is among Durenberger's friends who say they admire him for his private struggles.

"Many men don't have the upbringing, the standards he did," Coe said. "He felt he wasn't living up to them."

Durenberger's standards are rooted in a devout Catholicism. He grew up in an almost monastic atmosphere, on the campus of St. John's College in Collegeville, Minn., where his father was for years the school's athletic director. From the Benedictine monks at St. John's as well as from his parents, Durenberger said, he inherited the values of the work ethic, the idea that "you put back into the world more than you take out."

From the Rev. Francis Fleming, the pastor of St. Olaf Catholic Church in Minneapolis, Durenberger said he learned something else. In the summer of 1984, Durenberger heard Fleming preach on the subject of "Love Thy Neighbor as Thy Self." He decided then, he said, "that maybe one of my problems was that I didn't love myself well enough to be a good lover of neighbor."

"Politics," Durenberger added, "is the wrong place for somebody who doesn't think well of himself or who has a very high self-esteem but a very low threshold for having this knocked out from under him. The old me was the kind of guy who could have his props knocked out."

When Durenberger first discussed these matters with Berg of The Minneapolis Star and Tribune, it surprised some of his friends back in Minnesota. Horner, who described his former boss as "very private, he keeps a lot inside himself," said, "I don't think he would have done that a year or even six months ago. Now he is much more willing to open up."

Berg's story was prominently displayed in the Sunday paper. It included a mention of rumors of a past relationship with a former secretary in his office, something Durenberger refuses to discuss. It also included the most critical view of Durenberger's marital problems: that he in effect dumped his second wife after she had completed the task of raising his four sons by his previous marriage.

Durenberger acknowledged to Berg that he had struggled over that possibility, but he denied wanting to end his marriage. In a more recent interview, he called his marriage "my most important relationship," suggesting that much in his more than year-long self-examination centered on how far his public life had taken him from his youthful roots.

"I am a married person," Durenberger said. "I believe in the sacrament of matrimony and the whole business. You don't go to St. John's and believe that anybody can get a divorce at the drop of a hat. That relationship still needs to be resolved, and it needs to be resolved in the most honest way possible."

Durenberger apparently has not suffered politically by his candid discussion of the problems in his private life. In a recent Minnesota Poll by The Star and Tribune, he won the highest approval rating of any elected official in the state. The reaction to Berg's story, Horner said, "was generally one of empathy."

Meanwhile, Durenberger remains at the Cedars because, he said, he has not found all the answers he seeks about his personal relationships, particularly that with his estranged wife.

"I'm asked periodically by Penny and others if there is an end to this, is there a point where we know what is going on in this relationship," Durenberger said. "Yeah, I'm sure there's a point, but I'm not at that point yet. The good news is that I'm not at the point so many people get to at the beginning of one of these things when they say it isn't even worth doing it."