The president of South Korea is on his way to a meeting with President Bush at the White House. The two leaders are expected to discuss serious differences over North Korea and the future of their countries' alliance.
In a speech to military leaders, Mr. Roh credited the alliance with the United States as the basis for South Korea's political and economic success.
The future of that alliance is expected to be a main topic of his conversation Friday with President Bush in the White House.
The countries once spoke nearly as one on security matters, particularly concerning North Korea, but during the past few years, the relationship has frayed.
The biggest cause of friction is North Korea and its year-long boycott of multi-national talks on ending its nuclear programs. Pyongyang says it has built nuclear bombs, despite previous international commitments not to do so.
Lee Sang-hyun is the director of security studies at South Korea's Sejong Institute. He says Pyongyang will be watching Mr. Roh's visit to Washington.
"And probably they will decide their next step based on what solution, what steps will be discussed between Roh Moo Hyun and George W. Bush," Mr. Lee said.
Although both presidents say they cannot tolerate a nuclear armed North Korea and are committed to peacefully resolving the issue, they favor different approaches.
President Roh favors engaging Pyongyang. Officials in Seoul are hesitant to pressure the North, fearful of causing the impoverished state to collapse, which would require the South to spend tens of billions of dollars to rebuild it.
U.S. officials prefer a stern line toward Pyongyang. The Bush administration has made it clear Washington will not wait forever for North Korea to return to the nuclear talks, and may resort to other options, including seeking sanctions from the United Nations Security Council.
Mr. Lee at Sejong Institute says there is speculation in Seoul that Washington will push Mr. Roh to agree on going to the Security Council.
"One possibility is that the Bush administration will deliver some sort of ultimatum to Roh Moo-hyun and try to convince Roh Moo-hyun into joining whatever decision the U.S. is making," he said.
There are other irritants between the two governments. President Roh is making South Korea's foreign policy more independent of Washington. He wants South Korea to play what he calls a "balancing role" in Asia. That alarms some in Washington, who interpret it to mean a more neutral stance toward the United States.
Washington, for its part, has made Seoul officials uneasy by reshaping its 30,000 troops based in South Korea into a lighter force that can be deployed around Asia.
President Roh has reservations about U.S. forces operating from South Korea in conflicts that do not directly involve the South.
At the same time, a recent U.S. decision to move about 12,000 troops out of South Korea has sparked fears of abandonment. On Thursday, some South Korean newspapers reported that Washington might withdraw all its troops if Seoul does not agree with U.S. plans for a regional force. But U.S. and South Korean diplomats rejected the reports.