SEOUL, South Korea (AP) _ President Roh Tae-woo on Thursday named a new prime minister and foreign minister and reshuffled eight other Cabinet posts in a bid to spruce up his party's image before next year's elections.

Ro Jai-bong, 54, a chief aide and former university professor, was named to succeed Prime Minister Kang Young-hoon, who reportedly asked to retire from public life.

Ro holds a doctorate in political science from New York University. He would be expected to lead South Korea's delegation in a fourth round of high- level talks on easing tensions with longtime rival North Korea, scheduled for February.

The new foreign minister was career diplomat Lee Sang-ok, the ambassador to Switzerland and a former vice foreign minister.

Cabinet changes were also made in trade and industry, labor, unification, information, sports, transportation, communications and education.

Presidential spokesman Lee Soo-jung announced the shakeup at a news briefing Thursday.

Park Seh-jik, chief of the Seoul Olympic Committee that staged the successful 1988 Summer Olympic Games, was named mayor of Seoul.

The changes were seen as an attempt by the governing Democratic Liberal Party to spur public support before local elections to be held in 1991.

Roh's five-year term ends in 1992. He has made dramatic progress in foreign relations by expanding Seoul's ties with socialist and former communist nations, but support for his domestic policies is at an all-time low.

Roh has changed the Cabinet several times since taking office in February 1988.

On Wednesday, the Agency for National Security Planning, a government intelligence agency, announced the arrest of 31 students on charges of forming a North Korean-directed organization that sought to overthrow the government.

It said in a statement that more than 70 other members of the Chamintong group were being sought and that the organization has about 800 members.

The agency said the goal of Chamintong - an acronym meaning ''independence, democracy and unification'' - was to form a unified Korea by 1995 under the leadership of North Korea's Communist chief, Kim Il Sung. It said the organization would resort to armed fighting if necessary.

The agency said investigations found that Chamintong has manipulated the Chondaehyop, a dissident student alliance, to stage anti-government and anti- American activities in the guise of seeking democratization.

The two Koreas have been separated since 1945 and fought in the 1950-53 Korean War.