Great imponderable: How many will vote?

Except for the last minute radio-TV blitz and the clicks of the levers in the voting booth, campaign '82 is nearly over. The outcome now hinges on who shows up next Tuesday to pull those levers.

Experts, ranging from the US Census Bureau to independent researchers, are predicting voter participation to level off, or else continue a steady decline that began two decades ago. The big question mark is the blue-collar worker, most threatened by the recession, and the 11 million unemployed, who normally vote in low numbers.

If these giants in the electorate are awakened, they could produce a big turnout and a big boost for their traditional favorite, the Democratic Party. But will they vote?

A visit to East Baltimore, a short drive from the Sparrows Point steel factories that have laid off thousands of workers, indicated that many of the unemployed will not. Even among those who planned to vote, few saw solutions coming from either political party.

''What's the use? I don't see where it would make any difference,'' said William Mills, a shipfitter in line at the East Baltimore unemployment office. He blamed both Republicans and Democrats for the current state of US shipbuilding. ''Go to Japan. That's where all the shipbuilding is at,'' he said.

''I don't feel like it matters for me,'' said Dawn Halcott, who was just laid off from a Baltimore insurance agency and plans to avoid the polls next week.

Unemployed steelworker Dennis Hughes said he used to vote, but he's abstaining this year. ''I was laid off when (Jimmy) Carter was President. It doesn't change whether the Democrats or Republicans are in.''

Among those who plan to vote, some do blame Reaganomics. ''I'm gonna vote to get the Republicans out of there,'' said William Cheeks, another laid-off steelworker. ''It can't get no worse than it is now. At least when the other party was there, people were working.''

And even in the unemployment line, the Republican administration has not lost all support. ''In the last election I voted for Reagan,'' said welder Rich Lohman, adding that he would vote the same way next time. ''It took 30 years to get this country where it is now.''

Curtis Gans, director of the Committee for the Study of the American Electorate, is watching such potential voters carefully. ''Should the working class and unemployed decide to get angry, we could have an increase'' in voter participation for the first time since the 1960s, he says. ''Unless that happens , we're likely to have a decline except in selected races.''

Based on primary voter turnout and registration this year, Mr. Gans says that the ''trend toward downward participation is going to continue.'' Voter turnout during nonpresidential years reached a high of 48.1 percent of the voting-age public in 1962 and moved down to a low of 37.9 percent in 1978, according to Gans's figures. Voting during presidential years is always higher, although it hit a new low of 53.9 percent in 1980, down from 62.8 percent in 1960.

However, Gans is hedging somewhat in his predictions for this year because of what he calls the ''volatile factor'' - the working class. ''If it gets angry, we could even have an increase. But if it is disillusioned with both the Democrats and the Republicans, and some are willing to give Reagan more time, decreasing turnout will be the order of the day.''

Unions and other groups are running get-out-the-vote drives to try to galvanize their forces. In Maryland, members of the AFL-CIO are finding in their mailboxes a letter warning, ''Over 11 million unemployed. Will you be next?'' and urging them to vote.

Despite evidence of lower voter participation nationwide, such voter drives apparently can succeed in some cases. During the Sept. 14 primary, the black community of Baltimore surprised the city by turning out in record numbers to oust an incumbent chief prosecutor in favor of political newcomer Kurt L. Schmoke. It was a stunning victory, and it came following a concerted effort by a number of local groups.

While in the past only 30 to 35 percent of the city's registered black voters turned up at the polls, in the recent primary 55.2 percent voted, says Herbert Trader, spokesman for the Committee on Political Equality. The committee was founded by a group of local businessmen trying to ''guarantee that the black community of Baltimore has political power commensurate to its numbers,'' says Mr. Trader.

Notonly did organizers run registration and voter-education drives, but they sent sound trucks into black neighborhoods urging residents to vote. On election day, a local restaurant owner handed out free chicken dinners to anyone with a stub proving he had voted.

Trader is predicting that the black-voter increase will continue next week. Mr. Gans of the Committee for the Study of the American Electorate seconds that prediction, saying that ''outside of the South, blacks are likely to show up in higher numbers in this election.''

The greatest voter participation, however, continues to come from the well-heeled communities, where education and incomes are high and racial minorities make up only a small percentage of the population.

Such an area is Montgomery County, Md., an affluent and politically aware suburb of Washington.

In Montgomery County, one must be tactful when trying to get out the vote. It isn't a good idea to tell residents, ''I'm calling to remind you there's an election next week.''

People in Montgomery would be insulted, says Brian Barkley, campaign manager for Rep. Michael D. Barnes, the county's Democratic congressman. Instead, the caller must approach the subject more gingerly, saying something like, ''So-and-so needs your vote next Tuesday.''

In fact, voter drives are so refined in the county that a campaign can buy from the election board a computerized list of those registered, complete with party affiliation, birth date, and frequency of voting. As a result, campaigns can zero in on voters they most want to reach.

However, even Montgomery County has not been spared from the general decline in voting.

Marie Garber, retired chairman of the county's election board, notes a 20 -year decrease in participation. ''I don't see any evidence yet that we have bottomed out. She says that the percentage of registered voters going to the polls has dropped from 86 to 77.8 percent in presidential years. She says that she regrets the drop, ''because the fuller the participation, the more certain is the mandate.''

In Montgomery County many residents say they feel they can affect government. Both political parties have relatively active organizations. The county government must hold five hearings in March to fit in all of the citizens who want to speak out on the budget, and a school-board meeting once went all night, adjourning at 7 a.m. But voting in elections continues to decline.

Analysts puzzle over the national drop in voting. Steven J. Rosenstone of Yale University predicts that as the US population grows proportionately older, voting will increase, since older persons tend to vote regularly. Meanwhile, he expects unemployment and economic problems to keep voters at home this year. Those who would be most likely to want to punish Reagan are unlikely to vote, says Professor Rosenstone, an authority on factors affecting voting.

He sees two problems with the current low voting rates. ''Clearly, if the turnout gets too low, there's the whole legitimacy question that's raised,'' he says. ''We may be getting close to it.''

Further, he notes that with low voter turnout, the ''bias is against the people at the bottom of the social and economic ladder,'' and so these people are somewhat underrepresented.

''It's a peculiar puzzle,'' says Donald Kinder, associate professor at the Center for Political Studies at the University of Michigan. He notes that while Americans continue to vote in lower percentages, studies show that they are actually more politically aware today than in the past.

''People don't look to the government for solutions to personal economic problems,'' he says.

Gans, of the Committee for the Study of the American Electorate, maintains that a pervasive ''pessimistic climate in the body politic'' holds back voters. ''If I'm a voter, what am I voting for?'' he says. ''Do I vote for Reaganomics that I don't believe will work, or for the Democrats, who either are not offering anything or are offering something that didn't work in the past?''

Richard Scammon, of the Elections Research Center, says that often voters turn away from the polls because a contest offers no real choice, as when two conservatives or two liberals are running. He also blames the drop in voting on the ''increasing injection of the courts into political decisionmaking.''

Another reason, says Mr. Scammon, is that the two parties are too similar. ''Politicians want to win,'' he says, so they move ''into the murky middle'' on issues.

Finally, says Scammon, Americans ''just don't feel that the problems which concern them are the kinds of problems that are susceptible to political answers.''