The meeting comes amid conflicting reports over North Korea's position on the six-party talks, which collapsed a year ago following disagreement with the United States over an aid-for-disarmament package.

China and the United States said separately Tuesday that North Korea had agreed to return to the talks, but Pyongyang a day later ruled out any new meeting unless Washington meets unspecified conditions.

The hardline communist state has been boasting about its nuclear arms capability, and US reports suggested it may even conduct a nuclear test.

South Korea, bound by a half-century-old military pact with the United States, and China have been sympathetic towards North Korea and resisting US plans to refer Pyongyang to the UN Security Council or impose crippling sanctions on the impoverished state.

The United States and South Korea also disagree on the timing of diplomatic and economic rewards to be given to North Korea if it dismantles its nuclear weapons. South Korea wants the carrots to be given upfront.

"I think Roh is going to ask for more carrots and Bush would probably be more accommodating, but he (Bush) is also expected to make clear that if they (North Korea) don't return and seriously negotiate, then there has to be consequences," said Ralph Cossa, analyst with the US Center for Strategic and International Studies.

"The North Koreans have always felt that at some point they would have to return to talks, but they don't want to be seen to be yielding to Chinese pressure and they don't want to hand South Korea a diplomatic victory," he said.

The last round of six-party talks among the two Koreas, the United States, China, Japan and Russia aimed at weaning Pyongyang off its nuclear arms ambitions was held in June last year.

But North Korea refused to attend the new round in September, blaming what it termed hostile US policy.

The differences between the United States and South Korea over how to rein in North Korea reflect a broader split in their alliance, including Roh's recent rejection of a joint plan for armed intervention in North Korea in the event of instability there.

"The United States and South Korea do have very serious problems, bilateral problems, and North Korea is merely a distraction -- and the lack of coordination on North Korea is one of the symptoms of this larger problem," said Balbina Hwang, a North Asia analyst with the conservative Heritage Foundation.

Other contentious bilateral issues are the sharing of defense costs and a plan for redeployment of US troops.

The United States stations some 32,500 troops in South Korea and just deployed 15 US F-117 stealth bombers there for four months of operations, in what is seen as a pressure tactic aimed at Pyongyang.

Hwang also said that the focus of the Bush-Roh summit should not be the breaking of any deadlock over North Korea.

"This is because what that does is mistakenly shifts the issue away from North Korea and makes the United States and South Korea the primary actors on resolving the issue with North Korea.

"The reason the North Korea issue is not resolved is North Korea, and to say the United States and South Korea need to work together to break the deadlock misses the point," said Hwang.

Fred Carriere, the executive director of the New York-based Korea Society and an experienced Korea hand, said the publicly articulated US and South Korean policies on North Korea appear to show an "unbridgeable gap."

"If you listen to what they say, the US side has all sticks, and on the other hand, the South Korean side has all carrots, and the opportunity for South Korea to balance it is lessened because of the distortion caused by the Bush administration's excessive reliance on sticks," he said.

"If the US side were more balanced, then the South Korean position could also become more obviously mixed," he said.