SEOUL, South Korea - The race for president here turned into a referendum on relations with North Korea on a tense final day of campaigning yesterday, as the two front-runners relentlessly pitched their sharply different visions of how to deal with a dangerous and impoverished neighbor.

"Inter-Korean peace and cooperation is not a matter of choice," said the acknowledged front-runner, Roh Moo-hyun, a liberal labor lawyer from the ruling Millennium Democratic Party. "The survival of 70 million people is at stake."

Roh's chief rival, Lee Hoi-chang, countered with a denunciation of engagement with Pyongyang, the so-called sunshine policy championed unsuccessfully by the outgoing president, Kim Dae Jung.

The credibility of that policy suffered a major blow recently, with North Korea's admission that it has been secretly building a nuclear weapons program.

"The clearest distinction between myself and candidate Roh is that I believe the 'sunshine policy' is a failure," said Lee, a dour 67-year-old former supreme court justice from the conservative opposition Grand National Party.

Other major issues have floated to the surface, including ties with the United States, in a race that is expected to be extremely close. But most of these issues have receded as today's election has approached, with South Koreans and the candidates stressing relations with the estranged northern half of this divided peninsula.

If ties with the United States have faded as a focus, however, the stakes in the election for American diplomacy in this region remain unusually high. Western diplomats here routinely pre-empt questions about the race with a vigorous pledge that Washington "will work closely with either candidate."

Most political analysts, whether Korean or American, say that a victory by Lee would mean that bilateral ties would continue relatively unchanged. A win by Roh, often described as Kim's political heir, could presage a lengthy adjustment period for both countries.

Washington's diplomacy on North Korea is traditionally conducted through the so-called troika of South Korea, Japan and the United States, close economic and military allies who long ago realized they can maximize leverage on North Korea by maintaining common positions, at least in public.

Japan made a flourish of solidarity this week with visits of its foreign and defense ministers to Washington, even though there remain substantial differences in the two countries' approaches. But for South Korea, differences with Washington have been out in the open for months and are growing.

They have been fueled in part by a popular campaign of protests against the presence of 37,000 U.S. troops, after the acquittal in a court-martial of two American soldiers who had accidentally crushed two teen-age girls with their armored vehicle on patrol near Seoul.

After several weeks of disquieting news, beginning with Washington's disclosure of Pyongyang's secret nuclear program, a rush of conciliatory signals out of North Korea this week seem to have been made at least in part with the idea of reassuring South Korean voters and bolstering Roh's standing.

Pyongyang restated its call for the United States to negotiate a "nonaggression pact" as the only way to avoid war on the peninsula. Then it agreed to a new round of family reunification meetings and announced that it had finished clearing mines on its side of the Demilitarized Zone, a major step toward restoration of rail service between the countries.