For three years, Democrats put aside their varied ideological passions and plotted the overthrow of the leader of the Reagan Revolution.

Now, for the Democrats, it's mourning again in America.

President Reagan quashed their plans for the Year of the Comeback by convincing the nation that America is back. He turned aside the new era of Democratic pragmatism with a campaign grounded in feel-good imagery and economic fact, producing a presidential sweep and gains for his party.

The campaigns of 1984 had their roots in the maneuvers of 1981. In the White House, Reagan set about putting the promises of his own ideological commitment into practice almost as soon as he took occupancy. In the clubhouses, meanwhile, the Democrats launched a marathon road-testing in search of a winner.

Democrats always gave themselves a choice: It was always Mondale Or -- . First came Mondale Or Kennedy: But Sen. Edward M. Kennedy (D-Mass.) took himself out of the running before the voting began.

Then it was Mondale Or Glenn: the smart money of the party concluded early that Sen. John Glenn (D-Ohio), centrist and hero, was the perfect candidate on paper; their strategy came acropper when Glenn was taken off paper and put on the trail, put on television, and then put back on the shelf.

So it became Mondale Or Hart: Sen. Gary Hart (D-Colo.) and his New Generation politics of New Ideas was better on the trail, better on television, but uncharted on paper. The argument between the Mondale Democrats and the Hart Democrats was never really one of ideology but of pragmatism: Was the nation turned off to the traditional Democratic ways of politics by coalition? Would a new Democrat of unspecified definition provide sharper definition to a nation that defines leadership as a mix of ideology and image?

For the Democrats, as early as 1982, activists in the first caucus and primary states were taking a turn for the pragmatic. A 'Candidate Who Can Win'

As a helicopter swooped over the New Hampshire woodlands, Kennedy got his first look in two years at the neighbor state that had dealt him a crushing defeat at the hands of Jimmy Carter. Next time he runs, he vowed, he will work at building that "special relationship" with New Hampshire. What he did not know was that on the ground, the political figure he was coming to visit, the co-founder of Draft Kennedy in '80, was not for Kennedy in '84.

"What the Democrats need most of all now is a presidential candidate who can win," said Dudley Dudley, the prominent New Hampshire Democrat. "Four more years of Ronald Reagan will be a disaster . . . . I just don't think Kennedy can win it." And so she said that she would consider the field without requiring a liberal litmus test.

During the Democratic midterm convention in Philadelphia, this spirit of New Pragmatism was also articulated with unmistakable clarity by one Sam Grillo, the Philadelphia ward heeler with the jack-o-lantern grin and patronage job. Grillo would never have thought to use such a word but he waxed eloquent on the subject of pragmatism when Mondale began regaling a private luncheon of the city's political elite with the esoterics of an economic recovery plan.

"That's great," interrupted the ever-earnest Grillo, "but tell me something, Mr. Vice President. On Election Day are we going to have any street money?"

In 1982, Ronald Reagan looked vulnerable -- probably more so than Carter had looked in 1978. Unemployment was horrendously high; Reagan's polls were perilously low. The nightly news was about soup kitchens, proud families on welfare, Mrs. Reagan's designer-clothes sprees and his administration's ruling that catsup is a vegetable for schoolchildren.

Early in Reagan's term, protective White House aides had given the president a seating chart containing reporters' names for a news conference. If he gets in trouble, they told him, he should just turn to his right, because that's where they had assigned the "known friendlies."

The midterm election of 1982 gave no indication that Reagan would wind up two years later on the threshhold of a personal and political popularity on a par with the Republican hero Dwight D. Eisenhower. Indeed, the only reason for mentioning Reagan and Eisenhower in the same sentence after Reagan blitzed the nation with a plea to "Stay the Course," was perhaps to say that, politically, Reagan had the coattails of an Eisenhower jacket. The Democrats captured 26 Republican House seats. The Rough Road for 'Mondale Or -- '

Throughout the long road-testing of "Mondale Or -- " it looked as if every time Mondale seemed to find a way to satisfy enough of the electorate, they would not stay satisfied long, be they Democratic voters in the primaries or a nation of voters in the fall. Mondale proved most vulnerable when he reached his highs -- before the New Hampshire primary in the beginning of the 1984 season, before the Ohio primary late in the season, before the August hiatus, before the second presidential debate last month. Every time he was doing well, he got cautious, and every time he got cautious he got his comeuppance. Even in the straw polls of 1983.

A year before the real votes were counted, Democratic Party officials in a number of states responded to the quest for pragmatism with the most impractical and wasteful of political exercises -- a year of officially meaningless straw polls at their state conventions. They were viewed by the media and therefore by the field of Democratic presidential candidates as command performances, and so the exercise wasted candidate resources and opportunities as they struggled to create differences among themselves, and then to magnify those that they found.

The unity produced was mainly a revulsion at the events that the cognoscenti like to call cattle shows.

"We're just sides of beef," Glenn complained after being stampeded through his first straw poll in Sacramento. Hart, who had herded George McGovern through the antiwar realities of 1972, couched his disdain of the straw polls in terms of a new generation of celestial reality: "They are fixed constellations in the electoral firmament."

There was one moment when the straw polemics produced front-runner Mondale's first lesson in the dangers of overconfidence -- when Sen. Alan Cranston (D-Calif.) beat Mondale in the preference vote among 2,035 activists at the Wisconsin party convention. Never mind that he won by just 62 votes, after absurd efforts that included renting buses and even hotel rooms for delegates.

Forced onto the trail a year earlier than decency should dictate, the candidates at times understandably took a turn for the punchy. So it was that Cranston walked into the Sheraton Wayfarer Hotel in New Hampshire when a voter thought he recognized him. Cranston reached to shake his hand, saying, "I'm Senator Hayakawa from California." The voter brightened, "Oh yes, I'm a big fan of yours."

For the ever-recognizable Mondale, the front-runner's mantle was both an early essential and an early calamity. His high standing left him as the pack's lightning rod, as he wound up struck by the thunderbolts of every group and coalition he sought to embrace as his own.

Consider the incessant sparks between Mondale and the blacks. Mondale's problems began in Chicago when Harold Washington was angered because Mondale kept his promise to support Richard M. Daley, son of Chicago's late boss.

And in a cramped Atlanta motel conference room, an emotion-choked Mondale made the case he thought he'd never have to make before a group of concerned black leaders.

"We were together in every single fight," Mondale began, his often reedy voice soft and tremulous. "I was involved emotionally . . . I was perhaps the key person -- intensely, emotionally, involved . . . I'm surprised sometimes at how a record gets forgotten."

Jesse L. Jackson's candidacy siphoned much of the black support that would have been his -- and that loss would prove costly in the South, the Industrial North, and finally in California as Mondale found himself locked in his intraparty survival fight against Hart.

The candidacy of Jackson would pose other problems for Mondale as well. Jews, another bloc he considered his by political birthright, were angered by Mondale's slowness to rebuke Jackson for having made repeated references tinged with anti-Semitic overtones, among them his habit of calling New York City "Hymietown." Later, they would be angered for his slowness to condemn Jackson's own refusal to disavow black Muslim leader Louis Farrakhan, a Jackson associate, whose anti-Semitic comments were more explicit.

Reagan's strategists, meanwhile, found repeated opportunities to emphasize for television cameras his compassion for black youths. In 1983, the White House hastily recruited a Safeway grocery clerk and brought him to the Rose Garden in uniform just to stand behind the president while he presented a check to Washington Mayor Marion S. Barry for summer youth employment.

And this year, the Reagans dropped in for dinner on a black youth who the president said had become his pen pal.

The Democrats went into 1984 with a race that loomed as a struggle of Hollywood, Fla., versus Hollywood, Calif. Mondale went down to that Florida city to accept the endorsement of the AFL-CIO, while Glenn hoped that the movie "The Right Stuff" and his campaign's use of television ads and message strategy would prove a stronger political weapon than the money and manpower advantage that was Mondale's. Indeed, the year proved that in presidential politics, strong television messages could out-muscle traditional organization -- but it would be Hart, not Glenn, whose strong performances in the televised debates and the evening news would take the measure of Mondale's organization.

On the eve of the Iowa caucus, Hart was one of the few who saw it coming. He leaned over the dinner table at the Hotel Savery restaurant -- mess hall for the nation of visiting pols and press for weeks -- to whisper a prediction:

"The big story of the Iowa caucuses is not going to be Mondale and it's not going to be me. It's going to be the collapse of John Glenn. I mean all the way -- right down the tubes."

And that's the way it was. Hart was heir apparent to the other half of the two-man race coverage. In the final days of the New Hampshire primary, Mondale, confident of victory, took off to campaign in Maine and Vermont. Hart looked strong on the news each night -- his best pitch came not with a new idea out of a white paper, but with an ax at a woodsmen's festival. He threw the ax dead-center into a stump as the cameras recorded the feat.

Mondale was stunned in New Hampshire. Stunned days later when Hart captured Maine and Vermont. Stunned as Hart scored mightily on Super Tuesday -- coming within a hair of capturing Georgia, a defeat that would probably have led Mondale to take the step his aides had readied for him -- withdrawal from the race.

In the end, Mondale was rescued by the only thing that could stop Hart's surge: Hart. In Illinois, Hart fell victim to sloppy staff work, attacking Mondale for airing an ad that never existed, then trying to yank one of his own ads and finding he could not -- and all the while, Mondale used his "Where's the beef?" quip to turn Hart's hopes to hamburger.

During all the Democratic elbowing, the real political story of 1984 was happening not in Iowa or New Hampshire, not in the TV studios or the union halls. It was happening in those bureaucratic warrens where government economists compiled the statistics that left no doubt that recovery was at hand.

Unemployment plummeted, inflation stayed low, there were no nightly news scenes about soup kitchens nor interviews with middle Americans on welfare, and the vegetables schoolchildren were getting were vegetables.

In the White House, the president who is called the Great Communicator found he did not have to communicate at all. The news shows carried the good news -- and when they didn't, plump pocketbooks and weekly paychecks did.

For Reagan, 1983 had been a year of economic recovery and international debacle. His stationing of U.S. Marines in Lebanon turned a mission from futility into calamity when 241 were killed. But even as that horror was being relived, Reagan sent troops into Grenada to rescue American students and chase the communists out of control of that tiny island. And despite the Beirut tragedy, and controversy over U.S. military adventurism in Nicaragua, Americans began telling pollsters they felt good about what their president had done.

Reagan made a presidential art form out of turning defeat into victory. When House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) called for the Marines to be removed from Lebanon, Reagan summoned his fury, accused O'Neill of wanting to "surrender" -- and then a few days later announced that he was "redeploying" the Marines out of Lebanon and onto ships off the coast.

In May, the Reagan campaign officials would hold a news conference to proudly unveil their first round of "feel good" ads. Media critics poked critically at those smooth "It's morning again in America" ads, shot with soft-filtered lenses and gently lifting music, that showed Americans at work, building new homes, buying carpets for their present homes. But the public saw the ads as reminders of what they felt -- that things were indeed better, that America was in fact back.

This fall, Mondale turned his campaign rallies into Economics 101 seminars as he sought to educate the nation on the evils of the Reagan deficit.

Reagan turned his rallies into celebrations of the Olympics -- "Go for the gold," he said. He wound up his campaign with a half-hour televised address to the nation, heralding the American Olympic triumphs to show how America is back, standing tall. He had taken a nation that is fond of playing its politics like sports and taught it to play its sports like politics.

Mondale, while finishing gamely, never did master the video medium that dominated the year. Amid the primaries, NBC's Roger Mudd asked him, "What's your problem -- is it Gary Hart or Walter Mondale?"

Mondale replied haltingly about "my failure" to respond to charges. Mudd persisted: "How do you come across on TV?" Mondale, clearly uncomfortable, replied:

"I don't know . . . I'm not a PR type. One of the things that irritates me about politics is that they say, 'If you were only somebody you weren't, you'd really be hot.'"