Now that North Korea has made good on its threat with what appears to be a nuclear test, US military commanders and civilian policy makers are refining plans in the event that US President George W. Bush orders a blockade of North Korean shipments to prevent the sale of a completed bomb or nuclear components.
Senior officers say that Navy and Air Force combat and surveillance ships and planes are already in the region, and more could be deployed rapidly.
Still, any unilateral effort by the US to cordon off North Korea by sea and air could founder along the country's lengthy land border with China.
"This is a tough question," one senior official with years of experience in military planning said on Monday, speaking as did others on the condition of anonymity because he was discussing classified war plans.
"The only good options were before North Korea got the bomb. There are no good options now," he said.
For five decades, the US military has written war plans and deployed forces for a worst-case situation in the Korean Peninsula: a major artillery, missile and ground attack from north to south across the demilitarized zone.
But a conventional war is no longer the most pressing threat -- it is now nuclear proliferation.
Many staff officers contend that North Korea's ballistic missile and nuclear programs are not primarily intended as part of a plan for a land attack on South Korea.
If anything, North Korea probably regards its effort to develop a nuclear arsenal as a deterrent against an attack by the US.
The North Korean nuclear efforts could also be intended to press South Korea for diplomatic and economic gains and to put Japan, another important US ally, at risk, gaining even more leverage against the US.
Given this type of geopolitical geometry, US military officers and senior policy makers say, the Pentagon's abilities in the region, along with those of South Korea and Japan, are sufficient against the shifting North Korean military threat.
While land combat is not an imminent threat, Pentagon and military officials say, the prolonged deployments of ground forces in Iraq and Afghanistan have doubtless complicated planning for events on the Korean Peninsula.
Should more ground forces be required for South Korea, only a handful of combat brigades stand ready in the US, Pentagon and military officials say. To bolster the force, additional combat units getting ready for tours in Iraq could be pointed to the Pacific instead, with troops already in Iraq staying there longer than planned.
Although the decision to move a full combat brigade of US ground forces from South Korea to Iraq in 2004 generated much public debate on the peninsula, the Pentagon more quietly has shifted substantial numbers of heavy Air Force bombers and attack aircraft from the US to bases throughout the region to offset the decrease in ground forces. The Air Force's stealth bombers, with intercontinental range, are also available from their base in the center of the US.
Navy aircraft aboard carriers in the Pacific are on call, as are submarines equipped with a range of conventional and nuclear missiles. The most modern Patriot anti-missile batteries have also been assigned to the region, as well as Aegis cruisers with abilities designed to track and shoot down missiles.
"Taken together, this has added a tremendous amount of capability more appropriate for the threat right now," a senior US Defense Department official said.