REPEAT THREE times: Iowa does not have a presidential primary on Jan. 21, 1980.

What Iowa will hold at 8 p.m. next Monday are 2,530 precinct caucuses throughout the state. Both Democrats and Republicans will hold their meetings at the same time, in different places.

After all the Harris and Gallup reports on who's moving and who's slipping, Iowa will be the first real live test of actual voters making a decision on the candidates. And as such, the Iowa results will be analyzed, scrutinized and post-mortemized for at least two weeks, or until everybody can get to New Hampshire (which is the first presidential primary).

In 1976, only about 7 percent of the Democrats and 4 percent of the Republicans turned out for the Iowa caucuses. Unlike a primary, where participation amounts to quickly casting a secret ballot for your favorite candidate, a caucus requires both an investment of hours and a semi-public declaration of choice. This means that everyone else who attends the caucus in your precinct can determine which candidate you are supporting (just as you can see whom they are supporting).

Promptly at 8:30 p.m., in a given precinct, those Democrats who support President Carter will go to one corner of the meeting room. Sen. Kennedy's supporters will go to a separate corner, Gov. Brown's to a third corner, and the undecided voters to a fourth corner. Then the counting begins. Any candidate or group with more than 15 percent of those at the meeting is entitled to at least one delegate. (The number of delegates is apportioned to each precinct based upon the number of votes cast in the precinct for the party's nominee in the last gubernatorial election).

There will occur some swapping and switching after the first count. If a candidate's supporters do not have the necessary 15 percent, they might try to strike a deal with the uncommitted bloc to get one of its places for the county convention. The precinct meetings are only a first step in a six-month process -- precinct to county to district -- that will culminate in the state convention in June.

The candidates and their campaigns in Iowa face a major organizational job: to motivate, identify and inform their voters, and to convince them of the importance of spending a couple of hours in a school or a library on a cold night in Janaury. Much romanticizing has been done about the "grass-roots" activity in presidential campaigns; but in Iowa, a committed, competent "grass root" is worth more than the most creative, colorful television advertising campaign. Just because it's a caucus and not a primary.