Leaders of Korea’s two main parties are headed for a showdown following the final selection Monday of candidates to run in the four by-elections on April 29.

The latest approval ratings placed Moon Jae-in of the main opposition party and Rep. Kim Moo-sung, chairman of the ruling party at first and second, respectively, in the approval ratings as potential contenders for the upcoming 2017 presidential election.

Observers said the by-elections would serve as a barometer of Kim and Moon’s leadership as the parties wrangle over President Park Geun-hye’s economic and social reform measures.

Up for grabs are four constituencies ― Gwanak-B district in Seoul, Jungwon district in Seongnam of Gyeonggi Province, Western Ganghwa-B district in Incheon and Seo-B district in Gwangju.

The ruling Saenuri Party and main opposition New Politics Alliance for Democracy are expected to fight especially hard in the three Seoul metropolitan constituencies.

The NPAD faces a tough challenge in Gwangju, its traditional home turf, following a decision by Chun Jeong-bae, a party heavyweight during the Roh Moo-hyun administration, to run as an independent candidate.

The Saenuri Party, meanwhile, chose Oh Shin-hwan to run in the Gwanak-B district, while Shin Sang-jin, who represents Jungwon will run for reelection. In Gwangju, Chung Seung, the minister of food and drug safety, has confirmed his bid to run, and former Incheon Mayor Ahn Sang-soo has joined the race for the Ganghwa-B district.

The NPAD selected Jung Tae-ho to run in Gwanak-B, while Jung Hwan-seok will run in Jungwon and in Seo-B of Gwangju, Cho Young-teck will run for the party. Shin Dong-keun will confront the ruling party’s Ahn in Gwanghwa-B.

Though the by-election results have conventionally been favorable to opposition candidates, the Saenuri Party recently broke the jinx by winning in the July 30 by-elections in 2014.

Political researchers said that winning at least two out of the four seats will be inevitable for both Kim and Moon to secure their statuses as party leaders.

Kim Moo-sung said the governing party would encourage voters in their 20s and 30s to take part in the election.

The Saenuri Party also plans to consolidate the conservative votes by stressing the need to “expel followers of North Korea from the National Assembly” via speeches at colleges including Seoul National University in Seoul.

Moon Jae-in, for his part, plans to highlight “the incumbent administration’s failure in economic policies” and the widening income gap between the haves and have-nots.

For the Saenuri Party, it is considered a tough challenge to win in Gwangju and is instead focusing on winning the three metropolitan constituencies, pundits said.

Kim received 11.8 percent of the approval ratings according to the latest poll by Realmeter as of March 23.

Moon, who topped the list for the 11th consecutive week garnered 24.9 percent of support.

The NPAD faces a daunting task of placating the voters in Gwangju by quelling widespread disapproval among the Jeolla residents regarding the current party leadership held by figures hailing from the politically hostile Gyeongsang Province.

South Jeolla-based heavyweight Hahn Hwa-kap has publicly claimed that Jeolla Province should revive the region’s leadership status in the party, expressing his support for Chun, the former justice minister.

By Kim Yon-se (kys@heraldcorp.com)