In the end, after all the speeches, position papers and TV commercials, the fate of Toby Moffett, Senate candidate, may rest in the basement of a machinist union hall here with people like Denise Jean.

Jean, a bank accountant by day, is at night a cog in Moffett's sophisticated get-out-the-vote machine. She and a half dozen other volunteers spend their evenings on the telephone.

It's dull, tedious work, reserved for those at the bottom of the political totem poll. But it is crucial to Moffett's hopes of upsetting Sen. Lowell P. Weicker Jr., who led his Democratic challenger in the pre-election polls.

"It's close between Weicker and Toby, real close," said Jean. "It's important for us to get the vote out. That's all we can do now."

If history is a guide, only about 60 million of the nation's 170 million people of voting age -- about 35 percent of those 18 and older -- will go to the polls today.

Scores of races around the country hinge on the size and composition of the turnout. Traditionally, low turnouts benefit Republicans because their hard-core supporters are the most habitual voters.

This year, however, some GOP strategists fear that a low turnout could work against their candidates in some close contests, such as the Senate race in Virginia, because Republican voters -- especially small businessmen and farmers hurt by the recession -- appear lethargic.

Conversely, some Democrats worry that their blue-collar supporters may not be angry enough to go to the polls in sufficient numbers in states like Michigan, Illinois and Texas to enable the party to score hoped-for victories.

Democrats won landslide victories in off-year elections during the recession years of 1958 and 1974. And there are at least four factors -- all of which benefit Democrats -- that could drive turnout above the level of 1978, the last off-year election, when 34.5 percent of the voting-age population went to the polls:

* Unemployment and the off-year mobilization of labor unions.

* A combination of issues, such as nuclear freeze referendums in nine states, environmental concerns and women's issues, on which activists tend to be Democrats.

* Large-scale voter registration drives targeted at blacks and Hispanics, and increased voting by these two groups in the primaries in some Northeast and Midwest states. According to the Joint Center for Political Studies, 1 million new black voters have been added to the registration rolls this year.

* Increased voter interest. An Oct. 14 Gallup poll reported that 45 percent of the adult population had given "quite a lot" or "some" thought to the Nov. 2 election, compared with 39 percent at the same time in 1978.

There is wide disagreement, however, over whether turnout actually will increase. It has fallen in every off-year election since 1962, and the Committee for the Study of the American Electorate, a blue-ribbon group of political scientists, last week predicted that it will continue to decline in 1982.

What worries Republicans, who have put $1.3 million into a voter turnout campaign, is that, unlike the effect in most years, a low turnout today may work against them as much as a high one. They'd like a moderate turnout.

A recent Washington Post-ABC poll suggests why. It indicates that the 1982 turnout will be similar to that of 1978, and that older, better educated and more affluent voters will go to the polls in far larger numbers than other groups, just as they normally do. It found that only one-fifth of the unemployed can be found among likely voters.

This could be devastating to Democrats, who depended on the economically threatened to score landslides in 1958 and 1974.

"The key question this year is whether working-class unemployed are angry enough to vent their spleens at the polls," says Curtis B. Gans, director of the Committee for the Study of the American Electorate.

But the same ABC-Post poll reported ominous signs for GOP candidates.

Hard-core Democrats will be more likely to vote than hard-core Republicans. Women, who now are 52.4 percent of the electorate, will be more likely to vote than men. Blacks will vote in higher numbers than in 1978. A higher percentage of union members will vote than nonunion workers. And a higher portion of retired people will vote than any other group.

All these groups have major grievances with the Reagan administration. The same Post-ABC poll found that 62 percent of the nation's retired people, who favored Republicans candidates by 3 to 2 during the last two presidential races, intend to vote for Democratic candidates this fall, largely because of uneasiness over Social Security. Other polls find GOP candidates running 10 percentage points behind Democrats among women in many states.

Vince Breglio, director of the National Republican Senatorial Committee, describes the Senate race in Virginia between Rep. Paul S. Trible Jr. (R) and Lt. Gov. Richard J. Davis (D) as "dead even." But he says a heavy black turnout -- like the one that swept Gov. Charles Robb into office last year -- could tilt it to Davis.

In Rhode Island, Breglio says incumbent Sen. John H. Chafee (R) is well ahead in the polls, but "if there is a low turnout, we could be in big trouble. There is a segment of the Democratic Party that has rallied around the party label and is full of high-probability voters."

Here in Connecticut, neither Moffett nor Weicker backers know how turnout will affect their candidate. What they want is for the right voters to turn out.

For Weicker, a maverick Republican, the right voters are Republicans, independents and ticket-splitting Democrats. For Moffett, a liberal Democratic congressman, they are traditional Democrats, blue-collar workers, blacks, Hispanics and young liberals.

Moffett campaign manager Bob Hanson has devised a get-out-the-vote operation that divides the state into four main areas: heavily Democratic zones, swing Democratic zones, swing Republican zones, and heavily Republican zones.

Interestingly, both Weicker and Moffett have targeted the same voters -- independents in swing Democratic areas.