SEOUL - South Korea's two liberal presidential candidates agreed Monday to hold much-awaited talks over fielding a single candidate against conservative favorite Park Geun-hye for the Dec 19 election.

The move came shortly after independent candidate Ahn Cheol-soo finally agreed to sit down with Moon Jae-in of the center-left main opposition Democratic United Party, who has long courted Ahn to form an alliance.

The fate of the crucial December election, observers say, hinges in large on prospects for a possible merger between the two men, who are both seen as liberal alternatives to Park.

"I would like to meet with Moon so we can discuss our values and philosophies and agree on political reform measures," Ahn said during a lecture in the city of Gwangju in what was his first official response to the Moon campaign's proposal for merger talks.

The two plan to meet Tuesday by themselves without anyone else in attendance, according to Ahn aides.

Moon has consistently voiced hopes for merger talks since his primary sweep in September, as Park continued to lead opinion polls despite damaging controversies over the legacy of her father, late military strongman Park Chung-hee.

Ahn, a political novice whose outsider image appeals to disillusioned voters, had deftly deflected questions about the possible union and instead demanded the Democrats carry out political reforms before launching any merger talks.

A handful of key figures of the Democratic United Party, including nine Moon loyalists, have stepped down in an apparent attempt to meet Ahn's demands for political reform.

The election is slated for Dec 19, with incumbent President Lee Myung-bak constitutionally barred from seeking re-election.