WHEN Walter (Fritz) Mondale, the politician accused of lacking the necessary fire in his belly, stepped onto the mound and began hurling hardballs in the Democratic presidential contest, friends were delighted. Now the candidate was showing spunk, they said in calls that kept the family telephone ringing off the hook.
The one who wasn't so happy was Joan Adams Mondale.
''Oh sure, I think that adversity toughens you,'' she says. But she confesses , ''I don't like that kind of confrontation.''
When she first saw her husband jump from his seat and denounce an opponent's charges as ''baloney'' at the Democratic debate in Des Moines, she recalls being anxious. ''I was very worried because Fritz doesn't normally do that,'' she says. ''I mean, he's very measured and controlled. And that's because he's Norwegian.
''He's got Norwegian charisma.''
She laughs lightly as she sits in the living room of their modest house in Washington's Cleveland Park area. On its postage-stamp lot, the white stucco house hardly distinguishes itself from others in the aging neighborhood. A short climb up concrete stairs from the street level, one reaches its friendly porch, complete with swing and a brightly decorated pot that is a reminder of Mrs. Mondale's love of pottery.
The only hints that this house is out of the ordinary are the Secret Service guards and their surveillance camera panning from the front yard.
Inside, the Mondale home is a study in simplicity, with white walls and white furnishings and dark wood floors, which underlines the Scandinavian character of the candidate. Plants that usually add color died during December when the pipes froze, Mrs. Mondale says apologetically, and she has not yet replaced them.
For now Mrs. Mondale is occupied with slogging down the campaign trail five of every seven days, trying to help her husband, the former vice-president, become president of the United States.
But seated on the living room sofa just a few feet from a sleeping cat and sipping from a cup that she made at her potter's wheel, Joan Mondale looks the part of a hospitable next-door neighbor.
Her husband and she have been residents on the street since he was a new senator from Minnesota in the middle 1960s. She helped form a neighborhood vegetable co-op that involves taking turns donning jeans at 5 a.m. and going to the produce market.
Here she raised three children and volunteered at the nearby John Eaton public elementary school. (Later the Mondale children attended private high schools.) And here the Mondales made so many friends that a gang of 40 traveled to New Hampshire and went door to door recommending their neighbor to the New England voters.
''We felt so strongly about Joan and Fritz,'' says one of the volunteers, Barbara Rothkopf. She first met the Mondales through their mutual interest in John Eaton School, where Mrs. Rothkopf was once Parent-Teacher Association president while Walter Mondale was a ''very helpful'' PTA vice-president. But it was Mrs. Mondale who put in long hours helping out at school. ''I found her to be absolutely terrific,'' Mrs. Rothkopf says.
''She's an unusually thoughtful person,'' seconds longtime friend Bess Abell, who was Mrs. Mondale's top aide during the four years when her husband was vice-president under Jimmy Carter. Her former aide notes that in the midst of campaigning last year, Mrs. Mondale found time to deliver in person her Christmas gifts - pots she had made plus a family recipe for curry.
The daughter of a Presbyterian minister, Mrs. Mondale had an upbringing that was in spirit much like that of her husband, a Methodist minister's son. Both families were active Democrats and reformers who held strong ideas about racial equality. The Adamses, then living in Pennsylvania, switched their children to a Quaker school after the school had accepted a black pupil and been deserted by many of the white families. They did it ''to save the school,'' Mrs. Mondale says.
The Rev. Theodore Mondale and his wife, Claribel, living in the tiny hamlet of Elmore, Minn., regularly welcomed into their home visiting students from the choral groups of black colleges and took charge of finding housing for those they couldn't accommodate.
In economic terms, the two families were far apart, however. The Mondales had only a meager income from small congregations, and in summers their son, Fritz, sometimes had no shoes. The Rev. John Maxwell Adams, who headed the Presbyterian Church's college ministry, provided a cultured, comfortable life for his family and sent Joan to an exclusive girls' school in St. Paul.
Although she had dated mainly well-to-do Republicans, Joan fell for a Democrat she met on a blind date while he was a law student and she was a tour guide at the Minneapolis Institute of Art. Only 53 days (and 13 dates) later, they became engaged.
She says of her parents' reaction to her choice, ''They were greatly relieved. Oh, if I had married a Republican, it would have been a-w-f-u-l.''
From the start she knew that her husband had picked a career in politics, which meant working all day and campaigning on the side and being home infrequently. But she utters no complaints, noting that her father had been on the road six months out of the year.
The bond between the couple has remained strong. Mondale biographer Finlay Lewis writes that ''their marriage showed few of the strains typical of other political couples, in part because Mondale would often cut corners on the job to add hours to his time at home.''
A favorite family story harks to the day when Mondale sat in a Senate hearing , complaining to the late Sen. Philip A. Hart of Michigan that he wanted to see his son play a football game. ''Phil Hart said, 'Go, Fritz. I didn't, and I've regretted it,' '' Mrs. Mondale relates.
''And so Fritz left,'' she says, and drove to Sidwell Friends School, where his son William was playing for the St. Albans School team. ''And just as Fritz got to the St. Albans cheering section, William tackled a Friends player, and the two boys slid practically into Fritz's feet. William looked up and said, 'Hi, Dad.'
''It was marvelous. That was just perfect.''
All three children are now grown and are helping in the presidential campaign. Ted, who plans to attend law school, and William, now a senior at Brown University, are on the trail full-time, while Eleanor, who is trying to break into acting in New York City, is campaigning for her father on weekends.
Reviewing their years together, Mrs. Mondale reports, ''It's always been very stable and steady and predictable.'' When troubles arise, they discuss them ''rationally, intelligently, sensibly,'' she says. ''Everything's just sort of under control.''
The women's movement has touched Joan Mondale. ''Thank heavens for Betty Friedan and 'The Feminine Mystique' and thank heavens for the women's movement (activists) who said, 'Hey, now wait a minute. We're people, too,' '' she says.
But her own life style remains highly traditional, and her chief occupation now that her children are grown is that of a savvy political wife who knows how to help her husband's career. She recites the Mondale campaign lines with conviction.
She has delved deeply into her own interests, however, more than she might have without the new views of women, she says. She has written a book about her twin interests, ''Politics in Art.'' During the 1960s she took up potting, and today she shares a studio with three other potters.
Even with the campaign she usually manages to make it back to Washington Tuesday mornings for pottery class with teacher Vally Possony.
During her four years as second lady, Mrs. Mondale made the Vice-President's House, only a short drive from her current home, into a showplace for contemporary artists. She filled it with borrowed museum works and with original ceramic and glass works and frequently opened it to the press. Her energetic support brought her the unofficial title Joan of Arts. She says she will continue that role, along with focusing on the American family, if she and her husband move into the White House.
She also used her second-lady platform to speak out for women's rights and the Equal Rights Amendment, a fact that she now notes is forgotten. ''People don't identify me particularly with the women's movement.
''Maybe I wasn't outrageous enough,'' she opines. ''Maybe I should have been more sensational. I don't know. I'll try to do it better.'' Her laugh indicates that the minister's daughter will plot her steady course as in the past, without outrages or sensations.