Barack Obama and Hillary Rodham Clinton are expected to draw long lines and record turnout Tuesday as voters take advantage of a rare opportunity to influence the tight contest for the Democratic presidential nomination.

Sen. Obama, of Illinois, is the presumed favorite in the caucus because he was born in Hawaii and graduated from one of its high schools . Labor unions and prominent Sen. Daniel Inouye are backing Sen. Clinton, of New York.

The nature of a race without a clear front-runner earned the island state attention from both candidates, with Chelsea Clinton making a weekend visit and Obama's half-sister, Maya Soetoro-Ng, making daily appearances for his campaign.

"I don't recall Hawaii ever getting this much political interest from any national candidate," said Lisa Rosenlee, a political science professor who welcomed Chelsea Clinton to her University of Hawaii West Oahu campus class last week.

Obama has won the last eight primaries and caucuses held since Super Tuesday, Feb. 5. Clinton is hoping to stop that streak, but is placing more emphasis on winning delegate-rich states like Texas and Ohio, which don't vote until March. 4.

In a race where every delegate matters, 20 are at stake in Hawaii.

The count stands at 1,281 convention delegates for Obama and 1,218 for Clinton. It take 2,025 delegates to claim the presidential nomination.

Democratic Party officials predict heavy turnout at 68 caucus sites statewide, from rural farm houses to urban high schools. Only about 4,000 people participated in the party caucus four years ago.

Officials have ordered extra ballots as a precaution, and some worry that even those may not be enough for everyone.

Anyone who signs up as a member of the Democratic Party, even at the caucus itself, will be eligible to participate.

Results won't be known until late Tuesday night.

The 20 delegates will be awarded proportionally based on the caucus results. Another nine "superdelegates" from Hawaii -- members of Congress and party leaders -- will have votes at the national convention but won't be required to vote for a candidate based on the results of the caucus.

Clinton supporters waved signs in downtown Honolulu on Monday during the Great Aloha Run, while the Obama campaign held a Presidents' Day rally at a high school with Soetoro-Ng, Honolulu-born actress Kelly Hu and Rep. Neil Abercrombie.

"Policywise, they're both very similar. It's a toss-up," said Ian Chan Hodges, an undecided voter who asked Chelsea Clinton about patent legislation pending in Congress during one of her campaign events.

He said he'll probably vote for Obama, but his wife is leaning toward Clinton.

At Punahou School, where Obama graduated in 1979, some students who aren't old enough to vote have formed a club that has been handing out voter registration forms, distributing campaign literature and talking up their school's alumnus.

"People on this island are definitely noticing. It does give him an edge in Hawaii," said Kim Takinami, a 17-year-old member of Students for Barack Obama.