According to some reports, Jim Johnson is a clone of Walter F. Mondale. These reports are not true.

For one thing, Johnson is taller than Mondale. For another, Mondale sometimes wears colored shirts. Johnson doesn't.

Mondale is the one running for president. Johnson is the one running Mondale's campaign.

That exhausts the differences.

Both men are, it is true, Protestant Minnesota Democrats of Norwegian extraction.

But it is not true that they never disagree. They do disagree. "You know how they fight?" says one source who knows both men well. "They sit and stare at each other. Two Norwegians."

"I know what he thinks about thousands of things," Johnson says of Mondale, "and I know how he's likely to react to a lot of situations." Johnson knows such things because in the last seven years he has spent more time with Mondale than any other human being, with the exception of Mondale's wife, Joan. When Mondale was vice president under Jimmy Carter, Johnson says, "I was his shadow."

Mondale didn't pick Johnson to run his campaign simply because they share the same Weltanschauung or because Johnson knows what Mondale will want for breakfast without asking (tomato juice and black coffee). Mondale say he picked Johnson because Johnson is smart, thorough (to a fault some say), "ethical" and knows how to get things done.

And though you may never have heard of Jim Johnson, he is working on his fifth presidential campaign, his first as the man in charge. Those credentials don't put him in the public eye, but they make him known to Washington's political establishment, to labor union leaders and politicos all over the country. His imprint has been made in the circles where he operates, his visibility relinquished for the traditional anonymity of the good staff person. But with the presidential season again approaching, all of that is about to change. And if Mondale and he manage to beat the long odds in pursuit of the presidency, Johnson may well be the next White House chief of staff.

Johnson already has his share of trophies: he engineered the crucial Carter- Mondale victory over Edward M. Kennedy in the 1980 Illinois Democratic presidential primary; he was Mondale's road campaign manager in 1976, and he co-directed Edmund Muskie's only clear-cut victory (in Illinois again, in 1972) in what was otherwise a disastrous campaign.

Mondale refers to Johnson's "brilliance." John Reilly, a longtime friend and adviser to both Johnson and Mondale, says Johnson is "the best pol I've ever met . . . He doesn't understand just the delegate-selection process in Iowa or Washington, he understands how the issues play, what the messages are. Most people go past a Y in the road and make a choice in politics-- they become either an issues guy or someone who does nothing but politics; but the combination is unique."

At 39, Johnson is too old to be called a Boy Wonder. But he remains the embodiment of the clean-cut, earnest college student interested in good government and working through the system to change it.

He is frank to say that he wants power, and he has it, presiding over a growing staff of about 90 and a campaign treasury already approaching $10 million. Yet he is confident enough of his standing with Mondale that he invites other campaign aides who disagree with him on a major decision to take their case directly to the candidate.

Politics can be poker or it can be chess. Jim Johnson is a chess player. As a result, he has been criticized for being cerebral in what others see as an essentially emotional business. He is not, one critic points out, "sweating and ethnic" in the classic Democratic mold but is a man who fails to appreciate that political battles are won in the souls and not the brains of the electorate.

"I am not," Johnson says with monumental understatement, "what you would call 'trendy.'" This revelation comes from a man who invariably wears a white, button-down shirt with a rep tie, plain black shoes, a conservative, dark suit and horn- rimmed glasses. Although his curly hair is graying, his face is still relatively unlined, so he seems both youthful and mature at the same time. When he smiles, as he frequently does during conversation, his slightly prominent canine teeth give him the appearance of a puckish Count Dracula. In fact, despite the Organization Man appearance and reserve, Johnson has a droll sense of humor and is not above dropping an occasional expletive into his conversation or bluntly describing former Chicago Mayor Jane Byrne, for example, as a "total nut."

By reputation he has all the spontaneity of a diamond-cutter. He makes his way through the day consulting lists on a yellow legal note pad and 63/4 by 31/4 personalized index cards. Raymond Calamaro, a former Carter administration official and a partner in the law firm of Winston & Strawn (the same firm where Mondale's name is now on the letterhead), says that when Johnson gets up in the morning, "He lays his sentences out for the day."

Johnson works seven days a week now--12 hours a day during the week and earns a consulting fee of $3,000 a month from the campaign, plus a salary from his own company. His life is insular. Divorced after a brief marriage more than 10 years ago, he now dates Mondale's campaign press secretary, Maxine Isaacs. His apartment is directly across the street from his office, less than two minutes door-to-door. Johnson furnished his three-room duplex with tweedy, comfortable couches and chairs, Oriental carpets, contemporary art, objets d'art he has bought while traveling and five televisions (three color sets in his study so he can watch all three networks simultaneously, a black-and- white set in his bedroom and a Sony Watchman he displays with some chagrin, explaining that a friend brought it back from Japan).

He enjoys traveling and manages to get to London at least once a year. He plays tennis year round, eats out almost nightly and drives a bronze Cimarron Cadillac. He says he did not mind, when he worked in the White House, eating supper alone because--after 40 or 50 encounters in the course of the day--he suffered from "transaction fatigue, so that 'How are you?' at the end of the day becomes a hostile question."

It was foreordained that Johnson would go into politics: his family, his education, his experience, inevitably led him to where he is today. But was it also inevitable that he would choose to devote the better part of a decade performing, in his words, in the shadow of another man?

Despite the elegant taste reflected in his apartment and his penchant for travel, Johnson's origins were distinctly middle class. He was born and raised in Benson, Minn., "Home of Four Thousand Friendly People." Johnson's father, Alfred Ingvald Johnson, was a small-town businessman and a member of the Minnesota legislature for 18 years, served two terms as Speaker of the House and narrowly missed election to Congress in 1958. "I came from a very political family," Johnson explains. Almost every Saturday night A. I. Johnson's eight brothers and sisters got together, "and inevitably the conversation was politics."

Johnson has spent his whole life aiming in that one direction. "He was," recalled a Princeton classmate, Ira Silverman, "surely the most political of the students in the sense that he was involved in partisan politics and also in the sense that he aspired to be active in politics."

In the late '60s and early '70s, when other idealistic young men and women his age were still going into the Peace Corps, Johnson opted for politics at the national level, working in the McCarthy campaign in 1969 and the Muskie campaign in 1972. "It was sort of a micro- macro thing," he explahe brins. "I thought I could have more impact in changing things by getting involved in public policy--getting more money for the Peace Corps rather than being a volunteer in it."

Before working on the McCarthy and Muskie campaigns, Johnson was a vice president of the National Student Association. He has a bachelor's degree from the University of Minnesota and a master's degree from the Woodrow Wilson School of Public and International Affairs at Princeton University. (He also taught there and worked as an administrator.)

When Muskie all but dropped out of the 1972 campaign, Johnson--with the blessing of Muskie officials-- went to work for the McGovern campaign. He never felt comfortable there. The day after the 1972 Democratic convention ended in Miami, Johnson joined Mondale, who was running for reelection to the Senate and has been with him--or no more than a plane ride away--for the last 11 years.

He has taken the title of "acting chairman" of the Mondale for President committee. He now sits in a distant corner of Winston & Strawn law firm, not more than 10 seconds from Mondale's office. The "acting" designation, Johnson says, was his idea in order to give some Democratic luminary a titular role later on, but no one doubts that he is very much in charge of the campaign.

After Carter lost to Ronald Reagan, Mondale asked Johnson to stay close so that they could continue to work together. Johnson set up a political consulting firm, Public Strategies, with Richard Holbrooke, assistant secretary of State for East Asia under Carter and leased space from Mondale's firm.

The Mondale-Johnson relationship has none of the master-slave quality that often prevails between politician and aide in Washington. "It's a relationship that's pretty straightforward," says Johnson. "I clearly work for him. It's not that we're equals. On the other hand we've spent so much time together that we communicate easily back and forth, and I think there's a real minimum of my sort of shaving bad news or not confronting difficult subjects."

Johnson's style is too reserved to provide his friends with the stuff of hilarious or revealing anecdotes. That is not to say that he has no sense of humor. When asked to contribute to a recipe book, "Minnewaska Memories," being prepared for a family reunion, Johnson donated two of his favorites: "Hot dogs and Tab" and "Palm steak."

The Palm Steak: "Go to the Palm Restaurant at 1225 19th St., N.W., Washington, D.C. 20047. Wait to be seated. Tell waiter you would like a Palm steak. Wait for approximately 25 minutes. Eat steak. Pay waiter."

Jim Johnson likes control.

He does not like surprises.

He does not indulge himself by losing his temper. He is too measured to let go that way. When he speaks to a group of Washington political insiders, discussing the campaign, he uses only one- word references on a note card to guide him, yet his presentation sounds as though he were reading from a prepared text. Presiding over a meeting of the campaign staff, he controls the discussion, making sure that all points are heard without letting the meeting wander. Frequently, when he thinks a proposal has not been sufficiently considered, he invokes his favorite admonition : "staff it out"--shorthand for anticipating all the consequences before making a decision.

When decisions are needed, he is "not an agonizer," he says. "I make decisions very easily. I come down somewhere. I don't look back." His meetings begin and end on time.

Johnson's organization of the campaign frees him from daily details. He can take the longer view, trying --among other things--to strike the most productive balance in dividing Mondale's time between campaigning and raising money. For Johnson the equation is simple but crucial: Mondale has a finite amount of time. A campaign demands that the candidate make public appearances and that he raise money. Too much time spent campaigning can mean too little money. Too much time spentxplahe br raising money can mean too little exposure for Mondale.

Johnson is disposed by nature and by his job to be constantly calculating, a characteristic that is not always endearing. In negotiations, he concedes, "people find me capable of cold declarative sentences." He is also aware that Mondale's reserve may blur the candidate's image, "but whether more progress could be made through a hotter environment, I don't know. Who the hell knows? I mean the thing about Mondale is that Mondale likes politics. And if you go out with him, and he's mixing it up with the ward bosses or the unions or the people in the street or whatever, it feels like communication. It doesn't feel like pristine, namby-pamby s---. It feels like the real thing."

The question, Johnson says is whether his approach helps or hurts. "On any given day I either make situations turn out right or I don't make them turn out right." His own evaluation: "that it's pretty successful."

Johnson says he "feel strongly" about his political beliefs. When asked to reveal those deep convictions though, he becomes self-conscious "because you sound either like a Fourth of July speech or a Grade B movie about politics." He says he is worried about nuclear war and the country "being blown up," and discrimination of all kinds angers him. "There is a lot in me that makes me mad about that," he says. "It's pretty visceral."

Nonetheless, Johnson comes across not as the true believer but as the technocrat fascinated by the process--a man without passion.

That Johnson has devoted most of his time and energy over the past seven years trying to make Walter Mondale the most important man in America does not bother him. "I don't think my life is getting away from me, and I don't think I'm going to wake up one day and say, 'What have I done?' . . . If you said to me, 'Here is an alternative life,' or 'Here is an alternative career' or 'Here is an alternative way of doing all of this, which would you choose?' I have absolutely no question what I would choose: Working in the White House, working to elect someone president of the United States, having fun at it, and in the process standing up for what you believe in is--great. I wouldn't trade."