Two minor presidential candidates of the ruling Saenuri Party said Monday they have decided not to compete in the party's primary for the December race, as they consider it designed to comfortably select the long-time favorite Park Geun-hye.

Reps. Lee Jae-oh and Chung Mong-joon had called on the party leadership to fully open its primary voting to non-party members in what is dubbed an "open primary" system, to draw more public attention. The contenders, whose approval ratings remain in single digits, had indicated they would boycott the party contest unless the rules were changed.

On Monday, Lee, a close confidant to President Lee Myung-bak, said he will not compete in the primary scheduled for late August.

"I have said I will not participate in the primary if demands for an open primary system are not accepted," Lee told a press conference at the National Assembly. "To keep this promise, I will not participate in the Saenuri Party's primary with a heavy, bitter mind."

The former special affairs minister, who fought for South Korea's democracy movement, said he will continue to work to revise the Constitution to change the nation's five-year single presidency to a four-year double term presidency.

Chung, a seven-term lawmaker, also decided to give up his candidacy and will express his stance at a press briefing later in the day, his office said.

Chung, the controlling shareholder of the industrial giant Hyundai Heavy Industries, attempted to run in the 2002 race, competing with Roh Moo-hyun to become the single candidate to pit against the leading conservative rival. Although Chung promised his support for Roh after losing the primary-type race, he reversed his decision just one day before the voting day and later joined the then conservative Grand National Party.

The pair's withdrawal for the Saenuri Party's primary followed confirmation from party leadership it will stick to the former system that decides the presidential candidate based on a combination of votes, roughly half from party members and the remainder from the general public.

Thus far, the former interim leader Park has consistently led opinion polls on her conservative and liberal rivals.

Party officials have expressed concern a party primary with the near-unrivaled candidate will prove dull for media coverage, compared to the main opposition party's contest between several political heavyweights in the liberal camp.

The ruling party will open its three-day candidate registration on Tuesday and Park is scheduled to officially announce her bid at a popular shopping mall in Seoul that day. (Yonhap News)