South Koreans are voting for the nation's 16th president Thursday in an election overshadowed by anti-American sentiment and mounting concerns over North Korea's nuclear weapons. The two top candidates offer contrasting visions of the nation's future.

The polls are open across South Korea, where about 35 million people are eligible to vote. Current leader President Kim Dae-jung is nearing the end of his five year term. By law, he cannot run again.

The two leading candidates differ over Mr. Kim's so-called "sunshine policy" of engagement with North Korea.

Roh Moo-hyun of the ruling Millennium Democratic Party supports the position of the outgoing leader. The 56-year-old labor lawyer said Wednesday that inter-Korean peace is not a choice, but a necessity.

His chief rival, Lee Hoi-chang, candidate for the conservative Grand National Party, argues that dialogue should be frozen until Pyongyang dismantles its suspected nuclear program.

North Korea admitted in October it had a uranium-based nuclear weapons program, according to a U.S. envoy who visited Pyongyang. Last week, the North said it would restart an earlier nuclear program frozen under a 1994 agreement with Washington.

"What the North Koreans are saying is that they will try to instill a type of new fear into South Korean society which will in turn sway voters to vote toward Mr. Roh because he is more for dialogue, patience and initiatives towards Pyongyang," said Lee Chung-min, a professor at Seoul's Yonsei University.

On the eve of the poll, Mr. Roh, who has made remarks critical of the U.S., lost the support of Chung Mong-joon, his coalition partner and South Korea's popular football association president. Political analysts say the split could help Mr. Lee win more votes.

Anti-American sentiment in South Korea could also prove to be a factor in the polls. A groundswell of outrage was sparked by the acquittals last month of two American soldiers who were court-martialed after their armored vehicle hit and killed two Korean schoolgirls.

Although both candidates agree that the pact governing the 37,000 U.S. forces in South Korea should be changed, Mr. Lee has criticized the current government for neglecting relations with the United States.

In the run-up to election day, both candidates worked hard to appeal to South Korea's younger voters, who comprise nearly half of the country's electorate. Officials agree the race is too close to call.