WEST DES MOINES, Iowa — As the time to caucus approached, precinct captain Dave Erickson realized he had a problem: More than 100 people and one small room.

With eight precincts gathering at the West Des Moines high school, there wasn’t an empty spot in sight.

“I don’t know what we’re going to do. It’s going to be a challenge,” Mr. Erickson said. “It’s a great slate of candidates. There’s great interest in all of them.”

The scene at that caucus was repeated across the state as a record number of Iowans left their homes on a cold night and filled nearly 1,800 school gyms, fire houses, and community halls. Democrats estimated turnout at 220,000, and nearly 115,000 Republicans took part.

Democratic party officials worried that the crush of participants would delay the process, but most events appeared to begin on time. By late evening, Iowans had chosen Senator Obama and Michael Huckabee in the nation’s first test of the 2008 election.

“I know we are seeing incredible participation right now,” a spokeswoman for the Iowa Democratic Party, Carrie Giddins, said.

Anecdotes from across the state pointed to heavy turnout.

Amid the blur of activity at the West Des Moines high school, Michelle Obama made a surprise appearance in the cafeteria. The Illinois senator’s glamorous wife was mobbed by supporters and onlookers, but the school was so packed that even she melted into the crowd.

A Democratic chairman of one precinct in West Des Moines, Greg Nichols, said he had run out of his 250 registration forms.

Linda Lohse-Lange, of West Des Moines, has been going to caucuses since 1976. She has been a state delegate for both parties, but she showed up tonight in a bright red hat adorned with buttons for Mr. Obama.

“I had a hard time finding a place to park,” Ms. Lohse-Lange said.

The heavy turnout appeared widespread and in both parties. One Democratic precinct on the west side of Des Moines near Drake University had 444 participants, compared to 279 four years ago. A suburban Republican precinct in Ankeny had 220 people show up, compared to the roughly 100 that had been expected.

“It appears to be running high with new registrations a lot more than we had anticipated,” an executive director of the Republican Party of Iowa, Chuck Laudner, said.

At the West Des Moines caucus, Senator Biden was the lone candidate who didn’t meet the 15% threshold after the first count. That sent supporters of the other candidates scrambling over to woo Mr. Biden’s supporters.

Although they held tough at first, Mr. Biden’s backers ultimately scattered to other candidates.

Kevin Gilbert, of West Des Moines, came to the caucus undecided, but he ultimately joined the Edwards group. His wife, Sue, opted for Mr. Richardson.

“We’re dividing our loyalties, I guess,” Mr. Gilbert said.