The by-election race for Seoul mayor gained steam Friday as the strongest presidential hopeful vowed to help campaign for the ruling party while the unified candidate of the opposition bloc registered candidacy.

The Oct. 26 by-election pits Park Won-soon, a liberal lawyer-turned-activist with no party affiliation, against Na Kyung-won, the female candidate of the ruling Grand National Party, over the top elected office of Seoul.

Na continued to tout her policy vision for Seoul citizens, particularly the ordinary and underprivileged, by attending an athletic meet for disabled people on the day. Conservative groups supportive of the ruling party declared to help her campaign.

Park registered his candidacy with the Seoul Election Management Committee to launch his campaign committee. He also visited the Seoul City Council, controlled by the Democratic Party members, together with Sohn Hak-kyu, chairman of the main opposition party.

The upcoming poll is seen as a barometer for next year’s general and presidential elections. The race for the office, left vacant since Mayor Oh Se-hoon of the conservative ruling party resigned after losing the free school lunch referendum boycotted by the liberal opposition, is especially important as a quarter of the nation’s population lives in the capital.

Rep. Park Geun-hye of the GNP, former chairwoman of the party and considered the strongest contender for next president, has announced she will help Na and other candidates of the party campaign in the by-election race.

The decision came a long way as Park usually distances herself from party affairs and by-elections with much political risk at stake. Park, a daughter of ex-President Park Chung-hee, if elected, would be South Korea’s first female president. She lost to then presidential candidate Lee Myung-bak for the ruling party’s ticket to run in the 2007 presidential elections.

The ruling party hopes Park’s intervention in the by-election campaign will give a shot to Na, currently trailing Park in public opinion polls, in narrowing her gap further, Park is leading the race by nearly 10 percentage points. Party insiders expect the former GNP leader would step in the party campaign from the weekend.

Park Won-soon was selected as the unified contender running against the GNP through a vote against DP and other candidates earlier this week. Park, 55, is currently leading the race with an approval rating of around 45 percent, largely affected by the endorsement from popular software entrepreneur-turned-professor Ahn Chul-soo early last month.

By Shin Hae-in (hayney@heraldcorp.com)