The candidates together have spent more than $4.7 million on the race so far, making it the city's most expensive mayoral contest ever. Bainum has spent more than twice as much as Hannemann. Bainum has lent his campaign nearly $2 million, while Hannemann has lent his camp $90,000.

Bainum, 52, is a physician who's originally from Arkansas. He is campaigning on an "honest change" platform and promises to rid City Hall of undue influence he believes special interests have on city contracting and other decision-making.

Hannemann, 50, was born and raised in Honolulu. He says he is a more qualified leader because of his experience running the state Department of Business, Economic Development and Tourism during the administration of Gov. John Waihee, and other experience in Washington, D.C.

Both candidates have served on the City Council. Hannemann was chairman of the council, while Bainum chaired its budget committee.

Bainum represented the council district that stretches from Waikiki to Wai'alae Nui, and previously represented the Waikiki area during two terms in the state House that ended in 1994.

Hannemann represented the council district that extends from Halawa to Pearl City. He ran unsuccessfully for mayor in 2000, and ran unsuccessfully for Congress in 1986 and 1990.

Both candidates say they will improve city maintenance of roads and sewers, and pledge to seek a rail transit system to alleviate traffic congestion.

Many analysts believe the mayoral race is now close enough to tilt in either direction, depending on voter turnout.

Turnout is expected to increase substantially for the general election because it includes the presidential race. Each mayoral candidate insists that means more votes will go to him.

More than 17,000 voters backed Frank Fasi in the primary, and their votes for Bainum or Hannemann in the general election are also expected to help decide the race. Fasi, who was Honolulu mayor for 22 years, has endorsed Hannemann.

The presidential race also is expected to increase turnout among Republican and non-aligned voters. The mayoral race is officially nonpartisan, and both candidates are Democrats, but both are working to attract Republican and independent votes.

Much of the vote in the primary election split along income, geographic and ethnic lines, according to an Advertiser review of election results and demographic data.

East O'ahu neighborhoods with the highest income levels strongly favored Bainum, while those on the Leeward Coast and with the lowest incomes backed Hannemann, the data indicate. Middle-class voters, including those in several neighborhoods around the island's center, split between the two.

Votes along ethnic lines were less distinct, especially in areas with diverse populations. But Bainum carried several areas with the highest proportion of Japanese and Caucasian voters, while Hannemann carried those with the highest ratio of Native Hawaiians. Support was more mixed among neighborhoods with the most Filipino residents.