Iowa's Democrats have sent the nation three messages about Election '84: * Walter Mondale has moved so far ahead of his seven opponents that he could lock up his party's presidential nomination by mid-March.
* Gary Hart is emerging as the leading alternative candidate, especially among Democrats looking for a ''new face.''
* John Glenn's campaign, once expected to challenge Mr. Mondale right through the spring, has fallen into deep, deep trouble.
The Mondale victory in Iowa had been predicted by just about everyone. But few had expected it would be this big, this impressive. He outpolled the second-place finisher, Senator Hart, by about 3 to 1. He whipped Senator Glenn, supposedly his nearest rival, by 9 to 1. His combined vote was nearly equal to every one of the seven other candidates combined.
Mondale showed strength across the board. Data from an ABC-TV computer study which was made available to the Monitor showed that Mondale drew 46 percent of the vote in the state's largest cities. That was to be expected, since voters there are traditionally more liberal, more pro-labor, more activist - the groups known to be most solidly in the Mondale camp.
But the same ABC study found Mondale even stronger, with 50 percent of the vote, in the state's smallest communities, with fewer than 2,500 residents. And among farmers, he claimed 43 percent support.
His weakest showing - an area that other candidates may now try to exploit - was in middle-class suburbs, where his vote dropped to 34 percent.
This broad Mondale strength has suddenly turned the Democratic campaign into what looks like a one-man race.
A Democratic Party activist who has withheld his support from Mondale so far expressed amazement at how well things have gone for the former vice-president:
''I don't think Mondale's staff could have planned things this well if they had tried,'' he said. ''Look at what has happened: John Glenn has suddenly, unexpectedly faded. Who knows why? But it has happened too late for anyone else to take his place, too late for anyone else to mount a major campaign to challenge Mondale in the South, in the big Northern states, and so forth. It looks as if he can almost coast into the nomination from here.''
If there is anyone who can still play on the same field with Mondale after Iowa, it may be Gary Hart.
The Colorado senator, all but written off by the news media a few months ago, surprised some of the experts with a grass-roots strategy in Iowa that in the past has proved successful for others, such as Jimmy Carter.
Nearly complete returns for Iowa give Hart 15 percent of the vote. (Mr. Mondale got 45 percent, George McGovern 13 percent, Alan Cranston 9 percent, John Glenn 5 percent, Reubin Askew 3 percent, Jesse Jackson 1.5 percent, and Ernest Hollings 0.5 percent.)
How did Hart do it? There are several answers.
1. He invested time here. He spent 60 days campaigning in the state, 10 more than Alan Cranston, who was his nearest rival in that category. (Glenn was here only 32 days.)
Iowa is the kind of state where a candidate needs to meet the people, talk to them face to face in barbershops and gas stations, grocery stores, and private homes. Jimmy Carter did it. And Hart followed Carter's path, which led down long , lonely roads where you can drive 100 miles to meet only 30 voters. That kind of grueling work, however, can build great voter loyalty here.
2. Hart performed well in the two big debates seen on TV here. He was critical of Mondale, as was Glenn. But in criticizing Mondale, he created an image for himself as a candidate looking for new ideas, looking toward the future. That image took root with voters.
3. Hart positioned himself well for the type of voters who took part in the caucuses here. One study indicated this week that 50 percent of those attending the Iowa caucuses considered themselves ''liberal,'' 30 percent were ''moderate, '' and only 20 percent were ''conservative.'' Hart worked hard at winning over party activists, including women, the young, the elderly, and peace groups.
Hart's great difficulty now will be to keep his momentum going. He is reasonably well positioned in New Hampshire, where state coordinator Jeanne Shaheen has built what is considered the best organization of any campaign - with the exception of the well-financed Mondale team.
Beyond New Hampshire, however, the going could get harder. The Hart campaign has been so strapped for cash that it has been unable to get full delegate slates filed in some primary states.
The John Glenn story isn't so happy. In the early-morning hours Tuesday, as the Glenn team here sat around its almost deserted headquarters pondering what had gone wrong, it was clear that it felt this had not been its kind of turf.
Mondale, who comes from next-door Minnesota, was almost considered a ''favorite son'' by Iowa voters. Heavy support by labor unions gave Mondale a further advantage. And the Glenn forces were heavily outgunned in staff resources.
Sam Vitali, who ran Glenn's campaign in the final weeks here, observed that his staff in Iowa was outnumbered 162 to 37 by Mondale's campaign and that Mondale had union help besides.
Yet with all the disappointment here, there is no indication that the Glenn team will change direction as the campaign rushes toward New Hampshire, quickly followed by ''Super Tuesday'' primaries on March 13 in Florida, Georgia, Alabama , Massachusetts, Rhode Island, and Alaska.
Glenn sees his hope in what he calls the ''sensible center,'' the party's middle-road voters whose ideology falls somewhere between Ronald Reagan and Walter Mondale.
Glenn hopes that in a primary like New Hampshire, unlike the activist-oriented caucuses in Iowa, his performance will improve greatly.
The six other candidates generally had little to cheer about, either. Alan Cranston's strategists had stated that if he did not end up third here, it could seriously damage his campaign. He finished fourth. Reubin Askew spent 49 days campaigning in Iowa and hoped for strong support on from anti-abortionists. He finished sixth.
George McGovern got a strong vote -13 percent - for a third-place finish. But he is seen far behind in New Hampshire. Jesse Jackson and Ernest Hollings did little campaigning here, and came in at the bottom of the list.