(Yonhap) -- The lead held by South Korea's ruling party presidential candidate over her opposition rival has narrowed ahead of the Dec. 19 election, public opinion surveys showed on Sunday.

   In a two-horse race, ruling Saenuri Party candidate Park Geun-hye's lead over Moon Jae-in of the main opposition Democratic United Party (DUP) has been whittled down, in some cases to within margins of error, according to the polls. This change has come

after Ahn Cheol-soo, a popular software mogul, pledged to back Moon Thursday, weeks after dropping out of the race as an independent candidate.

   According to a survey by broadcaster SBS and pollster TNS Korea, conducted from Friday to Saturday, Park had 47.6 percent support from 1,500 adults. Moon earned 43.6 percent support, with a margin of error of plus or minus 2.5 percentage points.

   Ahn withdrew his candidacy late last month, after tough negotiations with Moon to field a single liberal candidate broke down. Then on Thursday, Ahn declared his full support for Moon.

   In an earlier poll by SBS and TNS Korea from Nov. 30 to Dec. 1, Park had earned 46 percent support while Moon had 37.8 percent.

   In another poll conducted Saturday by the mass-circulation Chosun Ilbo newspaper and pollster Media Research, Park drew 47.5 percent support from 1,000 adults, compared to 42.7 percent for Moon. The margin of error for this poll was plus or minus 3.1 percentage points.

   On Wednesday, a day before Ahn announced his support, Park led Moon  44.3 percent to 38.8 percent in the same poll. 

   In a third poll by broadcaster JTBC and research firm Real Meter, held on 2,000 adults Sunday, Park led Moon 50.6 percent to 43.8 percent, outside the margin of error of plus or minus 2.2 percentage points. Park's lead had been larger a day earlier, when she earned 51.1 percent support over Moon's 42 percent.