Twelve days to go.

As Walter Mondale's staff comes to the end of the longest presidential campaign in American history, as they stagger from a 5 a.m. baggage call in Kansas City to a midnight landing in Youngstown, Ohio, as they continue to insist that Sunday's debate was "a very decisive victory," they seem caught in a strange limbo between the all-out war they're fighting and the creeping sense, scarcely admitted to themselves, that they may well lose. If that sounds naive or incredible to all the voters who can't imagine they'll win, remember that before, even after Mondale lost New Hampshire, they always had time.

"I'm sure that I haven't come to terms with it," says press secretary Maxine Isaacs, talking on a late night flight this week from New York to Ohio. "Intellectually, I've been thinking about where I'll go on vacation and what I'll do about a job, but I don't think it's resonating emotionally for me. I don't feel we're going to lose . . . But I think there's some sentiment building. You suddenly look around and you've spent two years with these people, flying around in the middle of the night, arguing. Now the family's about to break up."

As Mondale ricochets across the country, from a rally with B.B. King in downtown Philadelphia, to a speech with Gary Hart at the University of Michigan, to a shopping mall in Burlington, Iowa, he attacks Ronald Reagan as "the most detached, the most remote, the least informed president in modern history." His staff members continue to live the same frenzied life they have for the past few years, eating dinner out of Ramada Inn junk-food machines, wondering when the next laundry stop will be, moving their "campaignapede" into cities via traffic-stopping motorcades that turn ground transportation into a surgical procedure.

But there's a difference. James Johnson, the campaign chairman, knows that what happens within the next two weeks may determine whether he'll be known as the man who managed the biggest landslide defeat -- or the biggest upset victory -- in American history. Less dramatically, he may simply be the person who in the end gave Ronald Reagan a good fight. "We still have a chance to come back," he says. "Win or lose, the dominant strain of analysis will be that Mondale acquitted himself well."

There are some in Washington's Democratic establishment who think defeat couldn't happen to a better group of people, since the Mondale campaign, like any campaign, has been criticized for what is considered a tight, arrogant circle around the candidate. But John Reilly, Mondale's longtime friend and adviser, argues that "if you're ahead, everybody is claiming how close they are inside, and if you're behind, they're claiming they can't get in."

Here is a look at three insiders -- with three different views of the Mondale campaign. The Corporate Man

James Johnson has run not so much a campaign as a corporation, managing an empire that has spent $88 million in the past two years. His staff, nationally, numbers 800. The week after the 1980 election, he sat down with Mondale and began planning his campaign to be president. Now Johnson is the long-range strategist, working not at the Wisconsin Avenue campaign headquarters but at his serene, tasteful office at the law firm of Winston & Strawn, right down the hall from the now silent office his candidate once used.

He is the Ice Prince, the cool, controlled Norwegian, disliked by those in Washington's Democratic establishment who consider him arrogant and ruthless, the Mondale extension who has managed to have most of the power and decision-making flow to him. In print, he is usually said to be "dating" Maxine Isaacs, although dating seems a ridiculous word for two people who haven't had a day off in months. "We see each other," he says, "and we have for several years." Campaign reporters sometimes refer to him as "Olaf."

The campaign, he says, has "changed me in the sense of how strong the ties are to the people who've gone through it with me. We've been through almost the equivalent of war. I don't think I've gotten at all cynical, although when you're doing something with this intensity, you're very conscious of who stands with you when you need help." He's in his office, looking out at the torrents washing over 26th and M. His phone buzzes constantly. "I'm not in," he tells his secretary.

As always, the last few days have been marked by inner tension, not the least of it with the Darth Vader of the Mondale campaign, pollster Pat Caddell. He worked for Gary Hart and repeatedly attacked Mondale during the primaries, but there he was on the campaign plane going to Kansas City, coming in as a midnight-hour adviser for the two debates. The campaign has muzzled him, insisting he not talk to reporters, but his presence is as much a signal of a last gasp as anything. "Listen," says Johnson, "what we're trying to do is win the general election. Just because Pat Caddell had been so negative on Mondale doesn't mean that he doesn't have good ideas, and can't be used as part of our strategy effort."

Of those in the tight circle of Mondale aides, Johnson seems the least emotional about the chance that Mondale will lose. "I work way ahead," he says. "My mind is almost always focused three, six months from now. I've already had to confront the possibility that this might not be successful."

But in Kansas City, just after the debate, Johnson took his place with the other "spin doctors," the advisers who talk to reporters and try to put their own spin, or analysis, on the story. In the huge press area in the basement of the Municipal Auditorium, Johnson gave his pro-Mondale argument and then ushered in McGeorge Bundy, the former special assistant for national security to presidents Kennedy and Johnson, who pleasantly told the press that the president "demonstrated to a national audience that on critical issues of fact and analysis he is out to lunch." Meanwhile, the Republicans had their own spin doctors at work, sometimes not even 10 feet from the Mondale forces. Among them was Lee Atwater of the Reagan campaign. When one reporter went to Johnson and said that Atwater was claiming that if the debate were "a draw," then Reagan had won, Johnson merely smiled.

"When Lee Atwater says, 'If it's a draw, we win,' that means the White House thinks they lost," Johnson said. Atwater, who was of course eavesdropping, couldn't take it. "A draw!" he yelled, breaking from his own cluster of reporters into Johnson's. "I didn't say it was a draw. Hey, we clearly won tonight! Let me tell you what Lee Atwater says." Johnson, cool as ever, just smiled.

His strategy in the next few weeks is to firm up Mondale's "base" in the industrial Northeast and midwestern "Rust Belt," areas that contain the millions of undecided Democrats who must be persuaded to vote for Mondale in order for him to win. The Reagan campaign has argued for months that Mondale made a crucial mistake by going to the South first and not shoring up his base early on, but Johnson disagrees.

"Talk about spin," he says. "I always thought they were saying that to keep us out of the areas where they didn't want us. Their argument was always that we should work on our base, and they should work on their base, and then they would win, 60-40. We've never considered the geography of this election to be very important. Mondale has to run in all regions. The notion that you could be doing really well in Michigan and not well in Pennsylvania didn't make any sense to us." Campaign Moods

Marty Kaplan thinks ahead only as far as the next set of remarks that Mondale has to make, frantically making changes on the computer terminal that sits in front of him on the Mondale plane. Behind him, two assistants rapidly make photocopies on a small machine in an aisle. "One thing I've always been jealous of is people who have the time for writer's block," he says, downing a Perrier in a mobbed Kansas City hotel bar a few hours before the debate.

His day usually begins at 6 a.m., when he digests whatever newspapers are available. He meets with Mondale and the other staffers from 6:30 to 7 a.m., having prepared the remarks the night before that Mondale will make that day. Mondale reads through them, usually asking for changes. Kaplan begins rewriting in the motorcade to the airport, then updates the speeches all day long, using news phoned in from the staff in Washington.

Kaplan is glib, the former president of the Harvard Lampoon, a former Marshall scholar, a former columnist at The Washington Star and a Mondale speechwriter during the Carter administration. He is also tall and balding, with two large tufts of hair coming from each side of his head.

"I am ambushed by good and bad moods," he says. "They're never in obvious sync with events. When the world says I should be despondent because of polls or bad stories, I can just as easily be fine. And similarly, when things are going brilliantly, I can get what amounts to postpartum blues."

The days right after Mondale's upset loss in the New Hampshire primary, Kaplan says he wasn't despondent. "It was one of those periods that was a paradoxical upper. I had a chance to help, since I could produce a speech that might contribute to a turnaround. My political value to the candidate was never higher. Let's face it -- when he's doing well, he doesn't need me that much."

Conversely, he says, "I think I was intermittently depressed in the period before the convention. I worked with him for six weeks on his acceptance speech, but the public perception of the success of the campaign in that period -- to put it mildly -- was minimal." It was a time when Mondale was being criticized for seemingly interviewing a representative of every ethnic group in America as a possible vice president, adding to the charges that he was a candidate of the special interests. "I had no control whatsoever," Kaplan continues. "I'm not part of the political decisions. I watched it play out, and I had the fear that my work wasn't going to make any difference. But there I was, trying to write the greatest speech of my life."

Like the others, Kaplan doesn't think they'll lose. "I can't see the historic landslide defeat as one of the options coming," he says. "There's a political ontology here. The nature of it all is that after a Mondale win, everyone retrospectively will be explaining how 'despite conventional wisdom' it all turned out the right way."

Later, when he was hanging around a makeshift press center in a University of Michigan reading room, Kaplan said he wasn't preparing himself for the emotional process of losing. "I went through the Carter loss in '80," he said. "I also went through The Star closing. I also, like most humans, have had romances end. There's a degree to which you can train -- and not train -- for experiences like that." Facing the Press

Maxine Isaacs has worked for Mondale since 1973, and this campaign, if he loses, will represent "the end of 11 1/2 years of my life. He won't run again. He'll be a lawyer." In 1976, when she was working for Mondale when he was running for vice president, she used to cry every day, usually at 5 p.m. when things seemed the worst. She doesn't do that anymore. "I feel like somewhere along the way, I grew up," she says. "It was like very big things didn't make me nervous anymore."

Isaacs is intensely loyal to Mondale, and is sometimes called "The Walking Press Release" by the reporters on the press plane who complain that her "spin" is an overly rosy view of the world. But reporters who might normally complain about a press secretary to a campaign higher-up don't do so in this case, in part because her relationship with Johnson makes some of them feel awkward. Isaacs herself admits that she is "not a professional press secretary. I'm a Mondale person. And we've been through a lot."

The campaign, to her, is "our opportunity. This is not Mondale running for vice president. This was our one chance to do this. I've been very conscious of that. I don't want to blow an important opportunity. It's such a rare thing. I don't want to look back and think, 'Oh, why was I so petty those last few weeks?' "

Isaacs admits that she'd "love to be White House press secretary," and says that after briefing reporters every day in Minnesota this summer, she no longer has a "phobia" about public speaking. She also says that "six months ago, I felt I had to be in the room for every conversation, every event," she says. "I was afraid I'd miss something. But I learned I didn't have to do that."

The worst moment for her came the week after Mondale lost the Maine caucuses. "It was terrible," she says. "It had never occurred to me that Mondale could lose it. Mondale had to go do the morning shows in Boston, and then do a commuter stop, and as we drove past Bonwit's, I said, 'I'm not going to do any more shopping until we win.' He looked at my clothes and said, 'You know, those things really go out of style in 20 years.' " The Campaign Lament

Like any campaign, win or lose, the staff is counting the days until it's over. Dayton Duncan, the deputy press secretary, has what he calls a "generic campaign paragraph" that is always said from one aide to another, in a bar late at night, in a distant city. It goes like this:

"So anyway. My marriage was in trouble. I thought it would be a good idea to see America, so I joined the campaign. I used to take pretty good care of myself. I got regular exercise, I watched what I ate, I only drank at social occasions. I was never one for one-night stands. As soon as the campaign is over, I'm going to get some rest and put my life back in order.