With the election three days away and polls asserting a commanding lead for President Reagan, "the crowd" has become a major salvation, sustenance and strategem for Walter F. Mondale's presidential campaign.

The candidate thrives on it. The organization practically runs on it. The strategists view it as a rebuttal to those pollsters and pundits who argue that Reagan has won, and they roll it out as a bandwagon for wavering Mondale supporters to climb aboard.

Mondale is drawing the crowds, large, enthusiastic throngs of listeners. They are turning out as at no other time in his long, frustrating quest for the presidency.

They braved the nippy early morning air in Portland, Ore., waited in line for hours in chilly Spokane, hung from street lights in Seattle and harborside balconies in Baltimore. They surrounded the city hall steps in Louisville and packed the convention center here this week.

They come in all colors, ages and styles of dress, although a large number appear to be under 40 and women seem to outnumber men. The majority do not suffer Reagan-Bush supporters lightly, and they relish Mondale's occasional putdown of hecklers.

"Give 'em hell, Fritz," someone inevitably shouts.

Mondale, these days, is standing up for Mondale. The man who took credit for moving his party to the center has found final political equilibrium back on the left.

His populism is unapologetic. "Mr. Reagan says that my plan is based on envy and limits opportunity," Mondale said in Spokane.

"I say that my plan is based on fairness and his is based on greed."

His speeches now are peppered with folksy idioms. Prepared texts are out, eye contact is in. The hollow one-liners, transparent applause lines and planned audience response cues have given way to narrative episodes punctuated by fist-shaking, finger-pointing warnings.

Mondale is politicking by parable.

His warm-up speakers are better these days, but often Mondale is his own best cheerleader. He trumpets every major newspaper endorsement as the sign of changing tides. He creates a tidal wave of burgeoning support by noting, often in error, that the event he has just left was the largest of its kind in history.

Not everyone in the crowd comes to revel in Mondale's newly enlivened rhetoric.

At a noontime rally in Louisville, stockbroker John Scott said he was "just taking a little time at lunch." He said he is sold on Reagan.

Business consultant Harvey Jacobs said he was there because the weather was "real nice" and to make certain he was doing the right thing by planning to vote for Reagan. His intentions were reaffirmed, he said.

But a few feet away, realtor Tony White held a large American flag on a long pole and shouted approval of Mondale's liberal litany as "the truth."

Computer supervisor Sherry Ross whooped and screamed and waved her red-white-and-blue "Mondale-Ferraro for America" placard, refusing, she said, to believe the polls.

Landscaper Geoffery Wohl said he came for some therapeutic hoopla, to satisfy himself that "I gave it my best try. I went out there and tried. I didn't sit at home and wait to hear the results on TV."

Secretary Dinnetta Holland said she was there giving Mondale a boost, "letting him know that he's got my vote."

Here in Buffalo, one-time police department aide Jimmy Smith, who had been in a public-works employment program scuttled by the Reagan administration and now makes his living as a gospel musician, said he came for the comfort of the crowd -- and found it.

Smith supported candidate Jesse L. Jackson through the July Democratic National Convention and switched to Mondale the next day.

"I came to satisfy a curiosity," Smith said after most of the 10,000 had left the hall. "Were there others? Were there white people in the same boat? . . . This showed me that there's a few hundred thousand who will vote the same way I will."

Lawyer Gerry Fornes said he came to stand up for his beliefs, views that he said others have been discouraged from expressing by the apparent groundswell for Reagan.

"I think that it support for Mondale might be less macho or something," he said. "If you're against Reagan, you're against America, you're against apple pie and baseball."

The increased size of Mondale's crowds is not all a spontaneous turnout or tricky arithmetic. As in the primaries, many are union members whose leaders have invested heavily in the Mondale campaign. And nearly every Mondale rally is scheduled for noon or after work.

At other times, Mondale simply inherits others' crowds. That was largely the case Tuesday night when most of the estimated 50,000 at the traditional torchlight parade presidential campaign kickoff in Chicago were foot soldiers of the city's ward bosses.

The rallies are designed to "excite Democrats" and "wake them up emotionally," a senior campaign strategist said, and to rev up voter turnout in key cities.

"These rallies show excitement and enthusiasm . . . on the streets . . . in some ways contradicting the polls," the strategist said. "They frankly have grown in size and enthusiasm beyond what we expected."