Iowa turns out to vote, but what's a caucus, anyway?

First, you vote. But if you can't settle things that way, well, just flip a coin to nominate the next president of the United States. That's the way it will work Monday night, when Iowa's 2,495 Democratic caucuses vote on the party's presidential nominee as Election '84 officially gets under way.

Caucuses, you see, are a little less formal, a little unorthodox, and potentially a lot more fun than the traditional presidential primaries that are held in most of the US. There are some interesting twists to the rules, which make the caucus a unique experience in American politics.

For instance, what happens if a precinct caucus meets to elect three delegates, and only one voter shows up? (More on that later.)

Or what if some precinct caucuses elect presidential delegates, but no one bothers to report the results to the state capital? That happened to the Republicans in 1980, and to this date no one is sure of the exact results.

Here's another caucus quiz:

Let's say you are at a precinct caucus in a rural town. Twenty-two people show up. They can elect three delegates. The caucus, however, splits 11 people for Walter Mondale, 11 people for Alan Cranston. If each group got its share, it would get 11/2 delegates. But the rules don't allow that. So what do you do?

Flip a coin. The winning side gets the extra delegate.

Unusual as that might seem, it's the way things will work here Monday, beginning at 8 p.m., central standard time, as the Democratic caucuses begin.

Caucuses, of course, are something of a mystery to most American voters. In fact, they are pretty mysterious to many Iowans, even though presidential caucuses have been held here since the 1800s, according to local officials.

Ever since about 1972, however, the Iowa caucuses have been getting more attention from biggies like CBS-TV and the Washington Post, and Iowans have begun taking them more seriously.

In 1976, when Jimmy Carter surprised everybody by winning the Iowa caucuses, about 40,000 Democrats attended. By 1980, when President Carter and Sen.Edward M. Kennedy hammered away at each other here, 100,000 Iowans showed up. This year's projected turnout ranges from 80,000 to 120,000.

All the action takes place right in the voters' own precincts. Each caucus is supposed to meet in a public building, if one is available. Sometimes, however, they have to squeeze everybody into someone's living room. It's all rather informal. This year, for the first time, you actually have to be a registered Democrat to take part in the Democratic caucuses. If you are an independent, or if you are not registered at all, they have special forms at each meeting to sign you up.

Once you get there, a few formalities have to be taken care of. A letter from the state chairman will be read. Something called the ''Party Contribution Envelope'' is passed around. Then there's a little pep rally for Tom Harkin, an Iowa Democratic congressman, who recently announced that he is running for the US Senate.

After that, the caucus selects a permanent chairman, and after taking care of a few other formalities, everyone's ready to vote.

At this point, each voter is supposed to take sides, depending on his own preference. Gary Hart people gather in one group, John Glenn people, Walter Mondale people, Reubin Askew people, and so forth in other groups. You can also go to an ''uncommitted'' group if you don't want to vote for any person, and in 1976, ''uncommitted'' came in first.

Now this is where a caucus can really get interesting. To stay in the running , each candidate must have enough votes to be what they call ''viable.'' In most caucuses, if a candidate doesn't have at least 15 percent of the vote, he's out of the running - at least in that precinct.

Let's say, for instance, Candidate X gets 11 percent of the caucus vote. He is then no longer in the running in that particular caucus that night. Anyone who voted for him can then switch to someone else. This possibility of switching could result in a lot of politicking in the caucus - which is exactly what is supposed to happen.

Finally, after certain candidates have been eliminated and each voter is counted for a ''viable'' candidate, the actual delegates are awarded based on a mathematical formula. The formula awards delegates on a proportional basis, so that if someone gets half the votes, he should get about half the delegates. Unless, of course, it's a coin-flipping situation.

It should all be over in about 90 minutes in most precincts.

There are, perhaps, just two other sidelights worth mentioning:

In 1980, there were about 10 precinct caucuses at which no one showed up. Not a single person. Zero.

That can present the party with some problems. They hope it won't happen again this year, but it's pretty tough to organize things in 2,495 different places on the same night and have everything run as smoothly as a John Deere tractor.

One other little point. It's always possible that there could be a caucus at which only one person shows up. What then?

Well, that person is the boss. He or she can elect all the delegates, single-handedly, then phone in the results to the state headquarters in Des Moines. It's all completely legal.

The precinct caucuses are just the beginning of the process in Iowa. From there, delegates go to the county conventions in April, then on up the line eventually to attend the national convention in San Francisco in July.