DES MOINES -- If the weather is halfway decent Monday, as many as 250,000 Iowa Republicans and Democrats are expected to go out in the frigid Iowa winter night in a process that could have a profound effect on who will become the next president.

Democrats will split into groups according to their candidate preference -- much like children dividing up for games at a birthday party.

Republicans will start their caucuses more traditionally with a secret straw ballot of their presidential preferences.

Some -- but not all -- officials of both parties have predicted record turnouts -- the previous high was 106,000 Republicans and 100,000 Democrats in 1980 -- because of the contested races in both parties. The state also has been organized as never before.

Still, even if turnout is 250,000, it would represent only about 15 percent of the registered voters of Iowa, a state that critics contend has a disproportionate influence because it is too small, too rural and too homogenized to be representative of the national electorate.

In addition, the precinct caucuses are only the first step in Iowa's presidential delegate selection process. They elect delegates to the county conventions, who elect delegates to congressional district conventions, who in turn choose the delegates to the state convention, which finally -- on June 25 -- will elect the delegates to the national convention.

Over the past four presidential elections, the Iowa precinct caucuses have replaced the New Hampshire primary as the first important presidential test.

They first gained national attention in 1972 because they were the first test of the Democrats' post-Chicago convention revisions aimed at weakening the party bosses' control of the nominating process.

In 1972, the caucuses gave Sen. George McGovern, who was the first to grasp their importance, his first boost to the Democratic nomination.

In 1976, they established little-known Jimmy Carter as a serious contender. In 1980, they presaged the failure of Sen. Edward M. Kennedy's challenge to the incumbent Carter and taught Ronald Reagan the danger of ignoring them. And in 1984, Gary Hart's surprise second-place finish here almost propelled him to the Democratic nomination even though Walter F. Mondale trounced him by 3 to 1.

This year, the caucuses of both parties start at 8 p.m. EST, an hour earlier than in the past.

Results from both parties will be reported immediately to the News Election Service (NES) in New York, which will make them available as they come in to the wire services and television networks. Officials of both parties expect a majority of the precincts to be reported by 11 p.m. EST.

In any event, the reports could seem confusing because three different results, in addition to any network projections, will be tallied -- the GOP straw vote, the Democrats' tally of each candidate's delegates, and -- because the Democrats refuse to do a straw poll -- an independent NES head count of the Democratic participants' preferences at each caucus.

The NES will try to have a reporter in each of the 2,487 precincts; it got into about 75 percent of the precincts in 1984.

The Democrats' delegate apportionment count differs from a straight head count because of the party rule that a candidate must have 15 percent of the participants at each caucus to be "viable" -- eligible for his proportion of the delegates to the county convention.

This results in a lot of political horse-trading. If one candidate, for instance, has only 11 supporters at a caucus that has 100 participants, those supporters must either recruit four others whose candidates are "non-viable," move to their second-choice candidates or be counted as uncommitted.

The outcome of such a process is hard for the pols and the polls to predict because no one knows how many people will overcome inertia, weather, baby-sitter and car problems to go out in the cold for several hours to stand up and be counted in front of their friends and neighbors.