JAKARTA - The two challengers for Indonesia's presidency started cross-checking electoral rolls on the eve of polling on Tuesday, after lodging complaints that the sprawling country's voter lists were riddled with irregularities.

Opinion polls have consistently shown that President Susilo Bambang Yudhoyono will trounce his rivals, winning a second term and a chance to quicken the pace of reform in Southeast Asia's biggest economy.

The objections to the voting process, led by Yudhoyono's challengers, former president Megawati Sukarnoputri and Vice President Jusuf Kalla, are not expected to derail the election.

However, analysts said the complaints could be a tactic aimed at fanning public doubt about the credibility of the process and pave the way for the losing contestants to challenge the result.

Security was stepped up in the capital, Jakarta, and other parts of the country on Tuesday because of fears that wrangling over the credibility of the register of some 176.3 million voters could spark protests in the world's third-largest democracy.

"People should not be confused, and this should not make the world view what is happening in our country as abnormal," Yudhoyono told reporters late on Monday, urging his rivals not to act improperly ahead of the vote.

A victory for Yudhoyono would most likely bring a renewed push for reform to attract foreign investment, create jobs and drive economic, which has slowed from 6.1 percent in 2008 and is expected to come in at between 3 and 4 percent this year.

If he wins the first round with more than half the votes, on the back of his modest success in tackling graft and the best economic performance in a decade, stocks, bonds and the rupiah are likely to surge on hopes of a more ambitious reform plan in his next five-year term and beyond.

Indonesian stocks and the rupiah have already rallied on the prospect of a Yudhoyono win this year, although some selling has emerged on concerns that Yudhoyono may be losing some election momentum and the vote could go to a second round.

The rupiah, the best-performing currency in Asia so far in 2009, fell 0.25 percent against the dollar in early trade on Tuesday. Indonesian stocks, which are up 50 percent so far this year, was trading up about 1.5 percent

Concerns over the voting process arose first in the run-up to the April 9 parliamentary poll, when duplicate and fictitious names were found on rolls and some voters found that they had not been registered to vote.

The Constitutional Court on Monday ruled that Indonesians who had not been registered could still vote on Wednesday by showing their identity cards, as demanded by Kalla and Megawati, partly defusing tension over the issue.

The pair's demand to see the voter rolls were also met late on Monday after they received soft copies.

The General Election Commission, or KPU, was ordered to sort out the problems before the presidential election and about five million more names have been added to the lists since then.

Arif Wibowo, a member of Megawati's campaign team, said volunteers and computers had been drafted into action across the country of more than 17,000 islands to help the KPU verify the list of voters and delete duplicate names.

The results of the checks were expected later on Tuesday, although Metro Television reported that about five million fictitious or multiple names had been found on the lists so far.

Despite their last-minute objections, Yudhoyono's opponents have backed away from earlier suggestions that they would ask for the poll to be postponed or might ask their supporters to abstain from voting.

(Editing by Ed Davies and John Chalmers)