Washington — Fifty-five million eligibles didn't vote in 1980, or 46 percent of the total. Stay-at-homes could decide the election again in 1984. That's one reason President Reagan visits a Hispanic-American veterans' group in El Paso, Texas, this weekend: to encourage the voters.
Democrats are trying to boost voter turnout, too. A new political system is coming into being, some political scientists say. Polls, press, and pundits now largely pick the presidential nominees instead of political conventions, they say. And the campaign continues for four years - it's an almost continuous process.
In the old days, there was a hiatus between presidential campaigns - it gave a breathing space. Today it's a continuous show. Also, voters expected a bit of melodrama at the quadrennial party conventions when the victorious candidate suddenly emerged. Today, conventions more often than not ratify popular choices already made.
Opinion polls and state primaries have stepped in. The ill-fated Literary Digest predicted a landslide for Alfred Landon over FDR in 1936 (based on 2.3 million post-card replies from 10 million sent out to telephone subscribers). It put the magazine out of business.
But now the ''scientific'' polls have been invented. Television also reaches everyone. The competitive pressure among electronic journalists to discover a pattern is overwhelming. In 1976, Jimmy Carter was proclaimed a ''winner'' in the Iowa caucus when he got only 29 percent of the vote, to 11 percent for Indiana Sen. Birch Bayh. Many felt this caucus made Mr. Carter the front-runner. Earlier, in 1968, President Lyndon Johnson got most votes in the New Hampshire primary, but a challenger, Sen. Eugene McCarthy of Minnesota, did so well that Mr. Johnson later dropped out of the race.
There has been a steady decline in voter participation in America. It has gone down like a flight of stairs: in 1964 the turnout was 61.7 percent; 1968 - 60.6 percent; 1972 - 55.4 percent; 1976 - 54.4 percent; 1980 - 53.95 percent. In 1984 - what? Most other democracies bring out 70 percent of voters or more.
Are voters asking ''What's the use?'' There are signs of confusion. The richest nation has a $200 billion budget deficit. Why? The Republican leader, President Reagan, is optimistic: He notes that the July unemployment rate has come below the double-digit line; it's down to 9.5 percent. ''Our economic policies are working. They are getting Americans back on the job,'' Mr. Reagan says.
Democrats attack: Look at interest rates, they say. By an economic process voters can't understand, the Federal Reserve Board puts on the anti-inflation brakes. Mortgage rates rise - they are about 14 percent. In foreign trade, the dollar is so ''strong'' that US exporters can't sell goods abroad. At the same time, in America, latest official numbers estimate 34 million are living below the poverty line, and the poverty rate now stands at 15 percent.
Election results depend as much as anything on the state of the economy. The unfortunate Herbert Hoover, for example, was overwhelmed by the 1929 crash. Today, foreign affairs may also play a big part. The President's recent activism worries some: James Reston of the New York Times, for instance, complains that Reagan is ''sending his fleet into the Caribbean and his planes into Central Africa. . . .'' The political consequences in 1984 will probably hinge on the result of the experiment.
A forthcoming book, ''Presidential Elections,'' by veteran political scientists Nelson W. Polsby and Aaron Wildavsky (New York: Charles Scribners Sons), argues that the organization of the parties is changing swiftly and radically: ''Over a relatively short period of time,'' they report, ''a new sort of American political system is coming into being.'' Among new features they cite are:
* A high degree of mass participation in hitherto elite processes.
* Replacement of political parties with the news and publicity media as the primary organizers of citizen action.
* Rise in influence of media-approved and media-sustained interest groups.
* Decline of interest groups linked to party organizations.