IN THE 1984 presidential election, 80 million adult Americans didn't vote. Next fall the number almost certainly will be higher. Voter turnout, as a percentage of eligibles, was only 53 percent, a slight rise from 1980; but the turnout rate in the 1986 off-year election was down from four years before. Ours is the lowest turnout rate of any advanced democracy in the world, and no one is quite sure why.

In the 1970s low turnout seemed a plausible consequence of the widespread negative attitudes and pessimism among voters and nonvoters alike. In the 1980s, when opinion has been more positive and sometimes almost sunny, you could argue that turnout is low because many Americans think things are going fairly well and see no urgent reason to vote. Yet even if you take that view, you probably find it perplexing that only a bare majority of Americans vote in our presidential general elections, and only minorities vote in other contests.

Can anything be done about low turnout? A recent study by Curtis Gans' Committee for the Study of the American Electorate provides modest but useful suggestions. New laws and regulations, it points out, cannot do much to change the attitudes -- angry alienation or soggy satisfaction -- that have accounted for most of the decline in turnout over the past 20 years. But they can do something to raise turnout at least marginally. Drawing on the experience of various states, the committee estimates that allowing voters to register on Election Day, as they can in Minnesota, would raise national turnout by 6 million over four years. Allowing citizens to register when they get their drivers' licenses, as they can in Michigan, would raise it some 800,000. Other methods are estimated to produce increases of different size: increasing the number of deputy registrars (2 million), having uniform registration hours and days (1.4 million), refraining from purging those who don't vote from the rolls (1.3 million), door-to-door registration(1.1 million), mail registration (only 255,000).

Not all these methods strike us as good ones. A state with a history of vote fraud should be reluctant to license deputy registrars or allow Election Day registration, for example. And a state must always be careful about tampering with an often fragile system of registering voters and regulating elections: this is one system where having zero defects is important. For that reason we're skeptical about federal legislation such as that sponsored by Sen. Alan Cranston and Rep. John Conyers mandating national mail and Election Day registration. Nor do we think most states will want to go as far as North Dakota, which has no voter registration at all. But we do suspect that many state legislatures can make registration and voting easier, without seriously increasing the risk of fraud. This is a good time, well before next fall's elections, for them to think about it.