While Democrats elsewhere offer theories on why two ultraright candidates in Illinois won primary elections last week, pollster J. Michael McKeon thinks one explanation lies just beyond his front door, in the blue-collar neighborhoods of this struggling industrial city.

Here, where jobless rates are 50 percent higher than the statewide average, McKeon said two years of political polling show continuing movement away from both national parties by union members and working-class voters beset by unemployment and crime.

Such voters, he warned Democratic leaders in Illinois and nationally last year, are "fed up with the way the two major parties handle crime and unemployment. This trend seems to accelerate in areas where major threats to their home and family exist."

In reports to Democrats and state labor union officials, McKeon had noted a correlation between concern about crime and an emerging blue-collar voter interest in candidates backed by Lyndon H. LaRouche Jr., a political activist denounced by numerous national politicians as a neo-fascist.

"In urban areas, 19 percent of registered voters list such things as burglary, robbery, home invasion . . . need for more police protection . . . as major concerns," he wrote in a May 1984 poll report for the Democratic Congeessional Campaign Committee. "In low-income and economically depressed areas, the figure rises to 23 percent. "

In another report, seven months later, McKeon noted that candidates backed by LaRouche had won local Democratic committee posts and a nomination for auditor of Will County in 1984.

So when LaRouche organizers showed up here weeks ago, leafleting motorists at Jefferson and Larkin streets, where Joliet's newest shopping malls meet the prairie, McKeon thought he saw the shape of things to come.

The March 18 Illinois primary victories of LaRouche candidates Mark Fairchild as lieutenant governor and Janice Hart as secretary of state on the Democratic ticket came as no real surprise to him, McKeon said.

"They the leafleters were getting insulted 10,000 times, but at 10,001, someone would listen," he said during an interview here. "They taught themselves how to talk to Joe Six-Pack. They started tapping into the feelings that are out here in blue-collar America."

Now, while Adlai E. Stevenson III, the Democratic gubernatorial nominee, struggles for a way to run for office without Fairchild as his running mate, McKeon finds reason to believe that with some 700 more LaRouche candidates running for local, state and federal offices around the nation this year, they will chalk up further primary victories.

"There is a mood of frustration and anger settling in deeper and deeper. These are people who have been left behind and can never catch up. They are vulnerable in all sorts of ways," he said.

"Somebody gets mugged and the whole neighborhood gets so mad they can't see straight. It's the kind of thing that dominates and dictates peoples' lives. And they are tough on crime and hate drug dealers. They'd like to see them all killed -- Ramboed. This is what the LaRouche candidates have been saying, too. Maybe the national politicians haven't been listening. But voters out here have."

In post-primary interviews, Democratic leaders around the state have taken a very different view, blaming their own lack of campaigning, voter apathy, a low turnout (less than 25 percent statewide), and rural dislike of the ethnic-sounding names of Stevenson's handpicked running mates: George Sangmeister for lieutenant governor, and Aurelia Pucinski for secretary of state.

Sangmeister won only 24 of Illinois' 102 counties, and Pucinski, daughter of a well-known Chicago alderman and former congressman, carried just three counties, including the heavily Democratic Windy City. Sangmeister won in Joliet, 35 miles south of Chicago; Pucinski lost.

Even where both Stevenson-backed candidates won, such as in Randolph County, leaders berated themselves for a poor performance. Said county chairwoman Barbara Brown, "Asleep at the wheel. No one realized who they Fairchild and Hart were. But it was not a reactionary vote. The ethnic nature of the names Sangmeister and Pucinski worked against them. There is a suspicion about Chicago and Chicago politics attached to the name Pucinski."

Here in Joliet, where the 1983 unemployment rate of 18.7 percent declined to 11.9 percent by the end of last year, people in random interviews stressed the lack of campaigning more than other factors.

"The Democrats didn't really back up their candidates, they didn't really push," said LaVon Uttley, a retired office manager. "It was a tragedy."

"I thought it was kind of hilarious about Stevenson," said Pat Sagadine. "I think it was an accident. Voters weren't sure and they're just picking names."

But in more than a dozen random interviews, no one here in this city of 78,000 would admit to having voted for Fairchild or Hart. One down-state party official said, "No one wants to admit it."

But McKeon said he believes this may be just the beginning of the emergence of LaRouche candidates, who espouse such stiff measures as death penalties for drug dealers, AIDS screening for all citizens, and quarantine for those with the fatal disease.

"What the national parties don't understand is the anxiety here," he said during a tour of the aging neighborhoods of a city that has lost about 7,000 jobs since 1979.

"Life here hurts. It's an anxiety you live with, but still, it's an anxiety. The LaRouchies know that you don't work the Gold Coast Chicago's most affluent area , where everybody's happy and they've got the American dream in their pocket. You come here."