Is it possible to improve long-term relations with both the US and China at the same time? South Korean presidential favourite Lee Myung-bak is about to find out. Mr Lee is widely expected to win next Wednesday's election to replace President Roh Moo-hyun, who must leave office after a single five-year term. Although Mr Roh has forged a new era of ties with China, he has at times rattled South Korea's traditional ally, the US. A more conservative, free-market figure than the man he is likely to succeed, Mr Lee and his Grand National Party are determined to rebuild the South Korea-US relationship while maintaining momentum in developing links with Beijing. Even while he talks up ties with the US, the dynamic former mayor of Seoul has already dispatched envoys to Beijing and other parts of the region, hoping to stage a diplomatic charm offensive in the wake of any victory. The challenges he faces highlight shifts in the security assumptions that have governed East Asia for decades. China's rise is forcing smaller nations across the region to consider fresh strategic interests. Over the past two years, for instance, China has overtaken the US as South Korea's leading trade partner. Beijing and Seoul have found other interests in common, both jointly criticising Japan's leaders over their approach to second world war excesses. The US, meanwhile, continues to keep 28,500 troops on South Korean soil to counter the lingering cold war threat from the Stalinist hermit state of North Korea. They are part of a continuing US presence that includes an aircraft carrier battle group based in Japan that makes it still the biggest military power in the region. The North Korean threat deepened after Pyongyang's first nuclear weapon test in October last year. And while China itself has grown concerned at the behaviour of North Korea, it remains its closest ally and a vital force in the international effort to create a nuclear-free Korean peninsula. South Korea has considerable interest in how Beijing uses its leverage. Across the region, governments and envoys will be watching how Mr Lee wades into an ever more complex diplomatic arena. 'Of course on paper, at least, a nation should be able to boost a wide range of ties and interests at the same time, but in reality things can be quite different,' said one veteran Asian diplomat. 'It could be said that Mr Lee will find himself between a waning superpower and an emerging one. It will be fascinating to watch how he handles it because we are all going to face similar situations in future. Nowhere are the issues quite as sharp as in South Korea.' Talking to a range of well-connected South Korean sources, it is clear Mr Lee is determined to keep the US-South Korean security alliance as the bedrock of his foreign policy. Any moves beyond and outside of that will be made with the alliance as the platform. On the campaign trail, Mr Lee has repeatedly tried to couch such a policy in pragmatic rather than ideological terms. 'I do support that the government needs to bolster the South Korean-US alliance because it will serve the nation's interest,' he said recently. 'I also said our country needs to build a strong economic partnership with China because it will help our economy grow.' That pragmatism is at the core of his self-styled 'MB Doctrine' - a rundown of seven principles to guide his nation's dealings with the region and the world. 'Diplomacy must not be based on partisan interest but on the national interest, with public consensus as its background,' it states. Those interests, the document suggests, place the traditional Seoul-Washington relationship at the core of South Korea's future - and not just on the security front. 'Shared values' surface - a phrase likely to be closely read in Beijing. 'Firmly anchored on their traditional friendship, South Korea and the US must reinforce and further develop the shared values between the two countries and their mutual interest,' it says. 'In the face of an entirely new international environment of the 21st century, we must forge together with the US a master plan for new strategies to ensure peace and prosperity not only in the Korean peninsula but in the wider East Asian region on the basis of liberal democracy.' There is less in the document on China. 'Existing ties with Japan, China, Russia and India must be strengthened,' it notes, also pledging enhanced co-operation with Southeast Asia, Australia and New Zealand. Hong Kong readers keen on South Korean movies, TV dramas and food will be interested to note Mr Lee's document also stresses South Korea's role as a 'cultural superpower'. On a more serious note, Seoul insiders also believe China will have a chance to play a key role in successfully de-nuclearising North Korea - the region's key short-term security challenge during the period Mr Lee might be South Korea's president. After progress on the long-delayed six-nation agreement and a recent burst of activity by the outgoing Mr Roh, Mr Lee is demanding a tougher approach to Pyongyang. The results of the better-than-expected October summit between Mr Roh and North Korean leader Kim Jong-il are almost certain to be reviewed to ensure South Korea is getting enough in return. The pair agreed to enhanced rail, tourism and fishing co-operation as well as a new economic zone and ship-building facility. Mr Roh has also been trying to forge a declaration of peace ahead of the formal peace agreement and diplomatic normalisation promised under the six-party deal. Such visions remain far off, giving a new government plenty of room to manoeuvre. The Roh administration had blueprints for an estimated US$20 billion in aid and investment from South Korea and Mr Lee's team can be expected to draw up similar plans. Already his policies include a vision for the bankrupt North to reach a gross domestic product of US$3,000 per capita over the next 10 years, with regional and international support. The difference may be in the desire to first get action from the North. Mr Lee ties progress to verifiable action on the complete dismantling of Pyongyang's nuclear programmes - work agreed to by China, the US, Russia, Japan as well as both North and South Korea. 'We must move away from the unilateral policy of appeasement that has been implemented without principle and embrace a system of reciprocity as a means to include North Korea's genuine opening,' the MB doctrine states. While it describes de-nuclearisation as 'essential', it adds other factors to the mix. Mr Lee's doctrine notes the need to solve the perennial problem of hunger and the need to support 'North Koreans' basic human rights and dignity'. 'If Chairman Kim Jong-il makes a decisive choice of giving up nuclear weapons and liberalising its economy, the international community will respond with an equally decisive choice,' his doctrine states. Such an approach is likely to find favour in Washington, where the administration of US President George W. Bush appeared decidedly lukewarm on Mr Roh's summit initiatives, given the need to keep Pyongyang focused on the six-party deal. In other practical areas, too, Washington may find Mr Lee an easier customer to deal with. Mr Roh has been keen for South Korean forces - now technically under US command in case of war on the peninsula - to be under local control by 2012. Mr Lee would probably be prepared to let that deadline slip if Washington was uncomfortable. Plans to gradually reduce US troop numbers may also face less pressure from the South Korean side. In private, Mr Lee has been making it clear that restoring trust between Seoul and Washington will be a priority. Whether he is able to build that trust elsewhere in the region is far from clear.