President Carter is expected to break the six-month logjam over leadership of the National Endowment for the Humanities today by nominating as its chairman Joseph D. Duffey, now assistant secretary of state for educational and cultural affairs.

Duffey, 45, who headed the President's Washington office during the campaign, said in an exclusive interview last week that he believes the role of the endowment should be broadened to more effectively influence a wider number of Americans, and that Humanities should take the initiative in developing a "public dialogue" to help redefine "national values."

Duffey will take over an agency with a budget of $111 million, and one which requires 79 words, beginning witht the phrase "The term 'humanities' includes," to define itself on official stationery. The post pays $52,500 a year.

Carter, in a speech last March, criticized the endowment for its "elitist image," adding that "we've got a need to preserve the quality of our programs . . . and expand opportunities for people who are isolated from them."

Humanities has also been under fire from Capitol Hill, where Sen. Claiborne Pell (D-R.I.), among others, argued that it has had a lesser public impact than its sister agency, the National Endowment for the Arts, which has a similar budget. Following such discussions, President Ford's renomination last fall of Fonald S. Berman as Humanities chairman was blocked in Senate committee, and Berman resigned when Carter was inaugurated. The term is four years, and opposition to the Duffey nomination is not explected.

Duffey, who has spent much of his varied career as a scholar, proposes no bold new programs. He says he plans to work through existing channels. "We would bring people and interest groups together on the issues. The meetings would sometimes be public and sometimes we would go to them." Other channels for leadership would be speeches and representations" and the "constant exchanges with Congress and other government agencies."

He points out as "an interesting model" the endowment's nationwide Bicentennial American Issues Forum, described as "the largest public participation program in the nation's history." He intends continued support for endowment-backed television series like "The Adams Chronicles," because they reach a mass audience.

Duffey said in the interview that in the wake of the 1960s, Watergate, technological change, the Vietnam War and other jarring events, America's self-image has been shaken, and that the public wants to reexamine "our understanding of ourselves." He sees this as a "new area" into which we have been evolving for some time and believes that "the federal government must take a role of leadership.

Joseph Duffey gives the impression of being a reflective, intelligent, adventurous and considerate man. He is an ordained minister of the United Church of Christ and his evangelical bent may account for the tendency in his conversation to dwell more on the spectrum than on particulars. Friends and associates characterize him with words like "philosophical," "a thinker," "a visionary," or "a dreamer."

Yet he refers to himself as "a political man." He is married to Anne Wexler, who is deputy undersecretary of commerce for regional affairs and economic coordination is also a member of the administration. His career includes a campaign for the Senate, which he lost in 1970 to Lowell Weicker, Republican of Connecticut. But the endowment, Duffey declares, is a place where "partisan politics is inappropriate."

He and his wife are accustomed to traveling in high circles, both in and out of politics, and they are familiar figures on the Washington scene.

Duffey's background contains many influences. He is the son of a West Virginia coal miner who became a barber after losing a leg in the mines.He is the first member of his family to go beyond the fourth grade. He was active in the civil rights movement. He participated in the antiwar "teach-ins." He worked for McCarthy in 1968 and for McGovern in 1972. And he was national chairman of the Americans for Democratic Action from 1969 to 1971 - its youngest chairman.

And, politician or not, Duffey's academic credentials match those of many scholars. He has a doctorate from Hartford Seminary, where he bacame an associate professor and was founder and director of its Center for Urban Studies. In 1971 he was a fellow at Harvard's John F. Kennedy School of Government and for the next two years he was an adjunct professor at Yale. Subsequently, he was chief exec utive officer for the American Association of University Professors.

When the rapidity with which he has moved from job to job prompted a question about the odds that he will serve a full 4-year term at the endowment, he replied: "I should certainly think so, particularly in light of my short tenture here at the State Department."

The nuts and bolts role of the Humanities endowment has traditionally been scholarly research - the job of three of the Endowments six central divisions (Fellowships, which means individual grants, Research, for group projects; and Education program, for grants to schools to improve performance in particular areas).

But the more public enterprises of the endowment have grown in recent years so that they now account for 47 per cent of the grants money. And the sizes of many of these grants tend to be large.

There was the $7 million American Issues Forum. There are the public television subsidies: "Adams Chronicles," $2.3 million; "The American Short Story," $2 million. There was teh series, for the Bicentennial, of individual histories of each of the states, at a cost of $1.4 million. Because the number of subscribers fluctuates, it is harder to put a figure on the widely published Courses by Newspapers, which for five years has provided credit course, in newspapers around the country, including this one.

Some of the larger grants touch on the arts: For instance the endowments subsidy of the popular show of artifacts from King Tut's tomb, now touring the country, though that may be considered archaelogy. And the endowment has helped underwrite several other major tours of art shows from abroad; museum assistance has been a traditional part of the endowment's work. But if these sound like arts, there are just as many projects at the Arts Endowment that could be called humanities.

There has been a tendency over the years at both endowments for each to play grantsmanship by merely choosing among proposals that applicants initiate. But there are signs that the endowments may be headed for less passive roles. The American Issues Forum, for instance, was suggested by Walter Cronkite to the White House. But the endowment designed and carried out the Forum. Asked if he planned greater initiative by the endowment, Duffey replied, "There is nothing in my philosophy to contradict that."

By last fall, Pell, who helped set up both endowments, was being blunt that he thought the Humanities Endowment was inadequately carrying out its charter under Berman, a Shakespearean scholar and a Republican.

The agency, Pell charged, and "faltered" to the point that it was "a pale shadow as compared to the Arts Endowment." Specific points of disagreement were sometimes murkey, but the basic issue was the Humanities Endowment's public impact - where the money should go and how it should be administered. According to an aide to the senator, Pell believed too much money was going to the "Eastern Establishment" and the states did not have sufficient control over their shares of the pot.

In Pell's view the statistics seemed to support charges of elitist bias. For the 15 months before last October Arts had issued double the number of grants as Humanities, even though their budgets were roughly similar (Arts: 5,050 grants out of $115 million; Humanities: 2,045 grants out of $111 million). Arts was simply helping more people, Pell argued.

Pell and Berman finally locked horns at hearings in September on Berman's renomination. Pell pressed his charges of "elitism" and the comparisons with the Arts Endowment.

Berman challenged Pell's premise. "Blessedly, arts and humanities are very separate and shouldn't be compared. We do very different things," Berman declared. He referred in particular to the broad audiences reached by Humanities - subsidized television programs. And on the issue of more state control of state grants - at the time states could make appointments to their Arts Councils, but not to their Humanities Councils - Berman said he feared politicization.

But the states got their increased control. Berman's renomination was shelved. He became a lame duck chairman. And the situation began that Carter was eventually to inherit.

The new President was said to express surprise more than once at the time he was spending during his first six months in office seeking the right person to run a rather specialized government agency that employs only 148 staff members out of a Civil Service of 2.8 million.

Carter met with Pell and Pell's House equivalent on cultural policy. Rep. John Brademas (D-Ind.), and then in early February set up an advisory screening committee. It was to this group that Carter made his pronouncement about ending "any elitist" attitude. The committee was told to "comb the country." One member got the impression that "it would be very nice" if this best person did not come from the East - given Pell's and the President's concern about links between endowment and the establishment.

The committee made a master list of 80 names while committee members found themselves lobbied by pressure groups. Potential candidates who seemed particularly attractive were invited in for 50 minute interviews.

The job interviewers were Elizabeth Sifton, a Viking Press editor and daughter of the late theologian Reinhold Neibuhr; Roger Kennedy, acting vice president for the arts at the Ford Foundation; William H. Goetzmann, a University of Texas professor; June Bingham, a writer and wife of Rep. Jonathan Bingham (D-N.Y.); and Hugh M. Sloster, president of Atlanta's Morehouse College.

Their decisions were not always unanimous; but a 4-to-1 vote was considered satisfactory as long as the dissenter did not feel strongly against the choice. The group ended up having to make four different recommendations to the President before a nominee was found.

Number one was Otis A. Singletary Jr., president of the University of Kentucky for the last eight years, a historian and a former director of the Job Corps in the Johnson administration. The offer came in early April without the President having spoken to Singletary, and after a 10-day wait, Singletary ruffled White House feathers by announcing publicly from Lexington that he was declining for "personal" reasons."

Within a few weeks the committee made a second recommendation, but that candidate also declined - because of "serious family problems."

Recommendation number three was very much an Easterner, Charles Blitzer, the Smithsonian Institution's assistant secretary for history and art, and a historian of the 17th century. Blizter was invited to meet with Carter in May. At the end of the discussion, the President asked him to put on four pages what his ideas for the endowment were. The papers were submitted, and it became apparent to Blitzer in some days that he would not be offered the job.

It was in June that the group finally recommended Duffey. He thought it over for about aweek and finally concluded, that it was a "challenge" he could not turn down. And, adds Duffey, "It helps to know that it matters to the President."

The endowment may not seem like such a colossus in the vast scale of the federal establishment, but in the world of humanities its chairman is a figure of power. TechnicallY, he is the only chairman of a 26-member National Council on the Humanities, composed mostly of scholars, but also including figures such as Warner Brothers chairman Ted Ashley and Mrs. John D. Rockefeller 3d. The chairman, however, really is his own boss, because the law requires only that he seek the "advice" of the council on grants; he may overrule them, and through the years chairmen have not hesitated to do so. Thus it was the chairman who in fiscal 1975 had ultimate say-so over the 6,800 applications requesting $302 million; and it was the chairman who controlled approval of the 1,330 grants worth $73 millions that were actually issued.

But the chairman must remember that he is his own boss only subject to the consent of the President and Congress.

It will be up to the new chairman to restore good relations with Congress, particularly if he is to get the money for the proposed extension to the endowment's public posture. On this subject Duffey evaded: "These are hard times to talk about money for anything."

There also has been speculation about merging the arts and humanities endowments for economy and efficiency purposes. That, Duffey says, "is something I am neither for nor against. I honestly haven't given it much thought.

Whether Duffey succeeds in giving the Humanities Endowment an egalitarian shot in the arm his stylish way of living may help counter the endowment's bland image. He and Wexler are on contract; before she joined the Atlanta offices, she was Washington representative of Rolling Stone, the rock journal.

And when asked if a post-election ski trip with their old Connecticut friends Joanne Woodward and Paul Newman might not be a first of its kind for a Humanities chairman. Duffey shrugged: "You know, that's not really our normal lifestyle, I just happen to be nuts about old cars, and Paul just happens to know a lot about them."