DES MOINES, Iowa (Reuters) - The long and sometimes arcane ritual of electing the next U.S. president begins on Monday in more than 1,100 schools, churches and libraries across Iowa, a state that wields political influence far greater than its small size.

After more than a year of up-close and personal evaluation of the candidates, Iowans will gather with their neighbors on what promises to be a cold wintry night to kick off the state-by-state process of picking the Republican and Democratic nominees for the Nov. 8 presidential election.

The starring opening-night role of the largely rural Midwestern state in the presidential drama, now four decades old, is a source of pride for Iowa voters, who spend months evaluating the candidates, looking them in the eye and asking questions.

“Iowans see it as a great privilege and a great gift. They take their role very seriously,” said Tom Henderson, chairman of the Democratic Party in Polk County, home to Iowa’s biggest city, Des Moines.

The caucuses will begin on Monday at 7 p.m. CST, and results are expected within two or three hours. Most gatherings will be in schools, community centers or other public locations, although at least two Republican caucuses will be in private homes and one Democratic caucus will be held at an equestrian center.

Turnout varies by community, with up to 1,000 people typically gathering in cities like Des Moines, while a few dozen or less may gather in more sparsely populated areas.

The state Republican and Democratic parties run their caucuses separately, although in some areas they hold them in different parts of the same building. Republicans will have more than 800 caucus sites, and Democrats will have about 1,100.

The two parties also have different rules. Iowa Democrats gather in groups by candidate preference in a public display of support, a tradition that can allow for shifts back and forth. If a candidate does not reach the threshold of support of 15 percent of voters in a caucus needed to be considered viable, that candidates’ supporters are released to back another contender, leading to another round of persuasion.

Republicans are more straightforward. They write their vote privately on a sheet of paper that is collected and counted at the site by caucus officials. A surrogate or volunteer from each campaign may speak to their neighbors in a last-ditch plea for support, adding to the uncertainty going into the process.

Neither party is offering voter turnout estimates this year, although many Iowans predict the Republicans will surpass the 121,503 who turned out in 2012. In the last contested Democratic caucus, in 2008, excitement over Barack Obama’s candidacy spurred a record turnout of 239,872.

Iowa, the 30th most populated state, and tiny New Hampshire, which holds the second nominating contest on Feb. 9, have traditionally served as early filters to winnow out the losers and elevate the top contenders for later contests.

But Iowa Republicans recently have had a spotty record at backing the ultimate presidential nominees. Neither the Republican winner in 2008, former Arkansas Governor Mike Huckabee, nor the winner in 2012, former U.S. Senator Rick Santorum, managed to win the party nomination.

Iowa Democrats did back the party’s last two nominees: John Kerry in 2004 and Obama in 2008, which ultimately launched Obama’s drive to the White House.