Lee remains a poll favorite despite renewed attacks from political rivals over his possible role in the 2001 stock price manipulation scandal.
If he wins, it would mark an end to the decade-long liberal rule by empowering the country`s conservatives.
The National Assembly on Monday approved a bill to launch an independent probe into the GNP candidate. Prior to the passage, Lee said he decided to accept the bill to help end partisan fighting that regressed into a fist-flying brawl in the National Assembly this week.
It followed the liberal United New Democratic Party`s disclosure on Monday of video footage indicating that, contrary to his assertions, he may have contributed to a financial scandal. The reinvestigation by an independent counsel is expected to start in mid-January, a month before a new president takes office on Feb. 25.
Presidential contenders yesterday toured Seoul to solicit votes before the curtain closed on their three-week campaign.
"It doesn`t matter how many special investigations I am subject to; the truth does not change," Lee of the GNP said, reiterating that the prosecution has already cleared his name.
Lee Myung-bak criticized the country`s largest political party, the UNDP, for resorting to "dirty politics" in Chung Dong-young`s "desperate attempt to grab power."
Chung, due partly to unsuccessful campaign strategies and partly to his link to President Roh Moo-hyun, who has grown exceedingly unpopular for his economic policies, has increasingly resorted to going negative against Lee. Polls taken last week showed a yawning 30 percent gap between the pair.
As another tactic, the liberal side has steadfastly defined the presidential election as a battle between themselves and "corrupt conservatives" who are represented by Lee Myung-bak. The GNP, on the other hand, claims it is time to end the rule of the "incompetent" liberals.
Chung yesterday called on voters to cast their ballots for the UNDP and himself in order to keep Lee Myung-bak from winning.
"I solemnly implore each and every one of our voters to come together to keep a lying, corrupt conman from becoming the leader of this country," Chung said. He also declared himself as the "de facto pan-liberal candidate" who should be considered as the sole candidate representing all the liberal camps.
Chung`s earlier attempts to forge alliances with Rhee In-je of the Democratic Party and Moon Kook-hyun of the Create Korea Party all failed because of clashing interests.
Some DP leaders have called on Rhee to quit the race and to help Chung gain a better footing, but Rhee shunned the request. He said he would complete the race.
Moon, formerly CEO of Yuhan-Kimberly, denounced the top two presidential candidates. He called Lee Myung-bak "corrupt" and Chung Dong-young "incompetent."
Independent Lee Hoi-chang appealed for right-wing support, saying he was the only "true" conservative candidate in the race.
He said, if he wins the election, he will form a government coalition with former GNP Chairwoman Park Geun-hye who is influential among conservative voters.
Lee Hoi-chang on Monday was spurned by Park who declined his request to visit her home. Lee Hoi-chang has desperately attempted to gain Park`s support in his quest for power.
The former GNP leader said if Lee Myung-bak wins, the entire country would be forced into further political chaos over the special investigation parliament is seeking on the frontrunner.
"That is why a criminal suspect should not be elected as president," the independent candidate said.
By Kim Ji-hyun