Stuart Eizenstat has a mezuzah on the door and an eagle on the mantelpiece. That's at home. At the office, the title is Assistant to the President for Domestic Affairs.

It's a title made - well, conspicuous - by John Ehrlichman in the Nixon administration, when it came to be associated with raw personal power. In the Carter administration, too, just about anything that can be classified as "public policy" or "issues" goes through that office.

But the search for Eizenstat's motivation for putting in regular 75-hour weeks at it bypasses dramatic individual psychology and gets diffused in two large institutions.

Religion and politics. The mezuzah and the eagle. A tradition of liberal Jewish community service, and a belief in the Democratic Party as the progressive instrument of change in the United States.

Repeated attempts to get Eizenstat to confess a passion - or even a preference - for any one of the issues on which he has worked always resulted in an even-voiced recitation of the entire Democratic Party platform (which he, as Carter's representative to the platform committee, helped shape).

"Passion," he said, is simply not an appropriate word. "I couldn't do my job if I looked at any issue with passion. I'm not a person of causes. It's my job to listen to the passionate people from both sides, to present the pros and cons, who's going to be for this and who's going to be against it, how do we sell it, and how do we get it across. Each issue contributes like a pebble in a mosaic."

He added slowly and, for him, recklessly, "But I do have a romantic attachment to -"

"To me," suggested his wife, Fran.

Eizenstat smiled. "To the Democratic Party."

"If anything would break up our marriage," said Fran Eizenstat, "it would be if I ever voted Republican."

Eizenstat, is an Atlantan, recently turned 34 years old, but his attachment to Carter was made cautiously, and after years of working for other prominent Democrats. For a year, he had a research and speechwriting job in Lyndon Johnson's White House. He was research director of Hubert Humphrey's presidential campaign in 1968. Later, he ran as a delegate pledged to Edmund Muskie.

When he talks about Humphrey, Eizenstat sounds like someone glowing with the reminiscences of the young fighting Humphrey in Minnesota: "When I entered politics, he was a hero of mine, the person I could most have faith in and admire." The year he's talking about, when he entered politics, is 1965.

Eizenstat grew up in Atlanta, where his father had a wholesale shoe business, and returned there to practice law after the unsuccessful Humphrey campaign. It's a life he plans to resume, and he talks about doing so in four years rather than eight. "We both sort of feel we've been to the mountain top," he said of himself and his wife, "but I'll be disappointed if I'm not the same person when I leave here as I was when I came."

Rep. Elliott Levitas (D-Ga.), whose family belonged to the same Atlanta synagogue as the Eizenstats, said they were both brought up to believe "that we got something out of this society, and we have to put something back in. This is why I'm doing this schtick, too. We don't need the ego trip."

Eizenstat describes himself as always having been "painfully shy," but he had always been a success - a student leader and basketball star with an "almost perfect" average at the University of North Carolina; Harvard Law School; and a partner in a prestigious Atlanta law firm four years out of law school.

He wanted to participate in Democratic politics in Georgia, and held several party offices as well as supporting the campaigns of Andrew Young and Maryland Jackson. But he was very careful about getting involved in the gubernatorial campaign of Jimmy Carter, "who had about as much chance of becoming governor and he did of becoming President," Eizenstat decided in 1969.

So he interviewed Carter. "It was the most sparse campaign headquarters I had ever seen - an old building with folding chairs and a few typewriters. The candidate was wearing an open shirt. He started to talk, and the talk lasted a couple of hours. I thought he had an amazing knowledge of urban problems - he could really talk my language.

"I saw him as a bridge between urban and rural Georgia. I was impressed. But I still was not decided after that first session - he was such an underdog, and I didn't want to invest my time in a candidate, however attractive, if he didn't have a chance."

So Eizenstat interviewed Jimmy Carter again. "The second time, I came away saying, 'By golly, I don't care if he has a chance or not, I want to work for him'"

But after the victory, Eizenstat felt "he had nothing to offer me," and went back to his law practice, his Democratic party work - he was one of the drafters of a new party charter in Georgia - and his service on the boards of various Jewish organizations.

In 1973, Carter asked Eizenstat to help him prepare issues papers for the Democratic National Committee to distribute to Democratic national office seekers. In his White House desk, Eizenstat still has the blue plastic 3-by-5 card file he used to alphabetize what he considered all the important issues and the experts who might provide advice on them.

In the spring of 1974, Eizenstat came up with "a wild hare" of an idea, and asked Carter to meet him for lunch in Underground Atlanta, the rather jazzily reconstructed old city.

"I think you ought to consider running for President," he informed Carter, who didn't say anything, but just smiled while Eizenstat characteristically ticked of reasons, by number, why he had proposed such a daring scheme. When he was quite finished Carter "indicated that he had already given it some thought. And he asked me to join what turned out to be quite an ongoing operation."

Eizenstat, who still had his blue plastic box, got himself a hand dictaphone. "I said, 'Let's take every issue I can identify as a likely campaign issue, and let's develop a coherent position on every one of them.' I would catch him during the day and say, 'Here is the thing about this I think is going to be controversial,' and after we'd discussed it, I'd dictate where we'd come out. We did 30, 35 issues, in about two days each."

For the presidential debates, Eizenstat prepared "three large, blackground volumes" of background material with sample questions and answers, a "pretty high percentage" of which were the questions actually asked on television Carter objected to "rehearsing," he said, but the two spent hours reviewing the material before each debate.

Now Eizenstat has on the average of three meetings a day with the President; attends all Cabinet and Economic Policy Group meetings and often those of the National Security Council. He works regularly on policy with congressional liaisons and Cabinet members, and keeps close touch with kep people from such groups as the AFL-CIO, the U.S. Conference of Majors and the National Governors' Conference.

"It was an intellectual challenge, but I was not drawn by the odor of excitement around a campaign, nor by the desire for a position," he said. "Never before did I take a position after a campaign. I can honestly say when I started this that I never expected to be in the White House. But as we got close to the end, I could more and more see myself being in a position to implement so many issues I'd worked on for so many years."

As Fran Eizenstat says - and they both say how much alike they are on issues and cutlook - "No matter what happened in that election, I couldn't lose. We're having a fascinating time here, meeting people who make history, but if the President has lost, I would have had an interesting job in Atlanta."

She was referring to the likelihood of her having been elected president of the Atlanta Chapter of the National Council of Jewish Women.

Fran Eizenstat, a graduate of Brandeis University with a master's degree in social work from Boston College, worked in the D.C. Health Department when they were last in Washington and on the Atlanta Model Cities Program in Atlanta. "It's been a real transition for me, because I've always worked, and I must say I'm tempted to get a job here."

But meanwhile, there is the hectic schedule of the political wife, whose husband of the political wife, whose husband works around the clock. To preserve some home life, he works at home from 5:30 to 7 a.m., in order to have breakfast with her and their sons, Jay, 6 and Brian, 4 before going to the 8 a.m. White House staff meeting.

He refuses all engagements - "unless the President needs me" - for Friday nights, when they observe the sabbath, and on Sundays during the day, when they're "very rigid about being together," often at the Jewish Community Center.

The children attend Hebrew school, are expected to contribute - "if only from their father's pocket" - to a charity box kept at home, and are told about social issues. "We don't lecture them," said Fran Eizenstat, "but on Passover, for instance, we'll talk about the concept of slavery, and people in the Soviet Union and the condition of blacks in this country."

And what do they tell the children if they want to know why their father has to be away at work all the time, "Well, you've got to remember that their basis for comparison is the campaign," she said. To them, just knowing that we're all in the same city is reassuring."

Eizenstat said there is no one accomplishment he would select in telling them why it was worthwhile to give up the time and activities together that they say they enjoy most. "I'm not over-romantic, but I'd say it was helping people move the possibility to achieve the American dream."

His definition of the American Dream - "the freedom, including the financial freedom, to do whatever it is you want" - is what they described themselves as enjoying in Atlanta. "Yes, we did - but then we wouldn't be helping others to achieve it."