The two opposition presidential candidates inched toward an agreement Thursday night on the format of an opinion poll to select a single candidate between them.

Moon Jae-in of the Democratic United Party and independent Ahn Cheol-soo were struggling to narrow their differences over the wording of the survey question.

The two sides came up with new proposals combining both positions, raising the possibility that a deal may be reached as early as Friday.

Ahn’s side favors asking respondents who they think would win against the Saenuri Party’s presidential candidate Park Geun-hye, while Moon’s DUP has maintained that the question should be designed to single out the individual that best represents the progressive bloc.

In the evening the DUP proposed a survey asking both who is more suitable as a candidate and who is more likely to beat Park. The method was first presented by a group of civic organization leaders as a compromise.

Ahn’s campaign immediately refused it, but later proposed an alternative measuring both their approval ratings and chances to defeat Park.

In a news conference Ahn’s spokeswoman Park Sun-sook suggested the two sides begin the survey as soon as possible.

“The two types of question in the survey are not free from problems of deviation and equivalence. But we do not have much time and the people are eagerly waiting,” she said.

She warned against any attempts by the DUP to rig the poll outcome through prior contacts with potential respondents via e-mail and mobile messages.

Moon’s camp responded positively. His public relations chief Woo Sang-ho said they will seriously consider the proposal from Ahn’s side. He said the negotiators should meet Friday without any conditions.

The two sides’ positions are thought to be a reflection of various survey results, which show that Ahn has higher ratings than Moon when pitted against Park, but the DUP candidate has stronger support as the progressive coalition’s candidate.

Gallup Korea’s polls for the third week of November showed that Ahn received 46 percent support while Moon was given 44 percent support in the scenario where each candidate competed with Park in a two-way race.

However, 45 percent of the respondents picked Moon when asked who they felt was more suited to represent the Ahn-Moon coalition. Ahn’s figure came in at 35 percent.

Earlier in the day Moon and Ahn met at a hotel in Seoul to try to hammer out an agreement that has so far eluded their negotiators.

They failed to yield any results from the one-and-a-half hour session, which was proposed by Moon during their live television debate on Wednesday night.

“Every effort needs to be made in the remaining time,” Moon said after attending a photo exhibition at Sangmyung University in Seoul in the afternoon. He declined to comment further, saying only that other commitments have been put aside to make time for the issue.

Following the meeting, Moon’s campaign spokesman Park Gwang-on said that nothing had been achieved and that the candidates were unable to “narrow their differences even by one step.”

By Choi He-suk (cheesuk@heraldcorp.com)