WASHINGTON - A truce stopped the fighting in Korea that once threatened to spread into a world war whose outcome might have been decided by nuclear weapons. Sixty years later, the costs of the Korean War continue to mount even amid relative peace.

Hostility lingers between the North and South and between the North and the United States, which still has no formal diplomatic relations with the communist nation in spite of the war's end on July 27, 1953. That ongoing antagonism is rooted in the U.S. commitment to take a leading role in assisting the South should war break out again on the Korean Peninsula.

Washington has tried for years to wean its ally off its dependence on the U.S. military by setting a target date for switching from American to Korean control of the forces that would defend the country in the event North Korea again attacked the South. That target date has slipped from 2012 to 2015 and, just this past week, American officials said the Koreans are informally expressing interest in pushing it back still further.

Another powerful legacy from the 1950-53 conflict is more personal for Americans: the seemingly endless challenge of accounting for thousands of U.S. servicemen still listed as missing in action. That mission, which competes for Pentagon resources with demands to also retrieve and identify MIAs from the battlefields of World War II and Vietnam, is beset with problems including bureaucratic dysfunction, according to an internal Pentagon report disclosed July 7 by The Associated Press.

What began as a Cold War contest, with the former Soviet Union and China siding with the North and the U.S. and United Nations allies supporting the South, remains one of the world's most dangerous flash points. In some respects, the security threat from the North has grown more acute in recent years.

So the U.S. is stuck with a lead wartime role in Korea and with a dim prospect, if any, of building the kind of relationship required to return to the former battlefields of North Korea to excavate remains of U.S. MIAs. The Pentagon says there are about 7,900 MIAs, of which approximately half are thought to be recoverable.

President Barack Obama marks the armistice's 60th anniversary with a speech Saturday at the Korean War Veterans Memorial.

The U.S. has kept combat forces on the Korean Peninsula since the fighting halted with the signing of an armistice, or truce, and it still has 28,500 troops based in the South. They are a symbol of a vibrant and important U.S.-South Korean alliance, and few advocate even a partial American troop withdrawal. But some U.S. military officers believe their permanence on the peninsula, with a singular focus on North Korea, is an anachronistic arrangement that should have been overhauled years ago.

The armistice agreement itself did not envision a long-term U.S. troop presence. It contains a passage recommending that within three months a high-level political conference be convened to negotiate the withdrawal of all foreign forces from Korea and "the peaceful settlement of the Korean question." That has never happened.

Bruce Bennett, a Korea expert at the RAND Corp., a federally funded think tank, says he believes the argument for giving Seoul wartime command of its own troops loses ground as North Korea's nuclear ambitions grow bolder. The North has tested nuclear devices and may be capable of mounting one on a ballistic missile - a worry not only for South Korea, Japan and others in the region but also for the United States.

"From the South Korean perspective - and I believe there is a lot of truth to their argument - having the U.S. in (the lead) is a strong deterrent of North Korea, and it means North Korea can't split the alliance," he said.

For similar reasons, some South Koreans favor asking the U.S. to reintroduce short-range nuclear weapons onto the peninsula. President George H.W. Bush withdrew all U.S. nuclear weapons from Korea in 1991.

In 1994 the South took peacetime control of its forces from the U.S. four-star general who heads a South Korean-U.S. Combined Forces Command, but the American general remained responsible for wartime control. In 2006 the two countries agreed that South Korea would assume wartime control of its forces in April 2012.

But in June 2010, shortly after North Korea torpedoed and sank the South Korean ship Cheonan, Seoul and Washington agreed to delay the handover of wartime operational control until December 2015. Now, U.S. officials say Seoul officials are again raising the prospect of another delay, although no formal request has been made.

Also on hold are U.S. hopes to send forensic science teams back to North Korea to find U.S. MIA remains. Although the North began to allow U.S. excavations in 1996, Washington stopped in 2005 amid rising nuclear tensions.

The mystery of what happened to MIAs in North Korea runs deep, as do the emotions of MIA family members who have petitioned the government, searched military records and in some cases pleaded with diplomats to find answers.

"It's that unanswered question that lingers year after year," says Richard C. Thompson of Chestertown, Md., a distant cousin of Gilbert L. Ashley Jr., an Air Force lieutenant who was one of five members of a B-29 bomber crew who became prisoners of war after surviving their shootdown over North Korea in January 1953.

Thompson and other relatives of Ashley and the other four airmen learned in the 1990s that they had been alive in the hands of North Korean captors after the July 1953 armistice was signed, but the men were never heard from again.

"It's a lingering melancholy," Thompson says.