When a dispute over several islets in the sea between Japan and South Korea threatened to spin out of control and into hostilities last year, the United States quietly intervened to tell both sides to back off.

"We told them that a bunch of rocks in the water weren't worth fighting over," said an American official, noting inflamed rhetoric and naval and air maneuvers around the isles, which the Koreans call Dokto and the Japanese Takeshima.

U.S. officials recognize neither name nor claim but refer to the isles as Liancourt Rocks, which a French whaler designated them in 1849.

This squabble over rocky isles may seem trivial but it reflects the deep antipathy Koreans and Japanese feel for each other. That, in turn, has a corrosive effect on the American security posture in Northeast Asia. The U.S. has defense treaties with both South Korea and Japan and has armed forces stationed in each. For America's allies constantly to be quarreling does the U.S. little good.

A senior American officer said the antagonism precludes joint planning and training in what, from a military viewpoint, should be a single, integrated area of operations. "It certainly limits our options," he said. "We have not found many ways to operate together."

Another senior U.S. officer carried that further, saying: "We don't talk to the Koreans about what we are doing with the Japanese and we don't talk to the Japanese about what we are doing with the Koreans."

Occasionally, Japanese and Korean officers get along personally. They cannot say so in public, however, because their compatriots would roundly criticize them. South Korean and Japanese navies sometimes do search and rescue drills at sea, out of the public eye, but rarely do they train together for war.

Moreover, American officers see little hope for improvement. "We don't see anyone on a path to resolve these issues," said a senior officer. "There's no political will in either country to resolve this, no substantive offers to even begin."

On the surface, U.S. leaders seek to be evenhanded. In reality, security relations with Japan are being upgraded while those with South Korea are being downgraded.

U.S. forces in Japan and Japan's Self-Defense Forces are organizing parallel commands. A Bilateral Joint Operations Coordination Center has been established and Japan's Air Defense Command is slated to move next door to the U.S. Fifth Air Force near Tokyo. The U.S. Army plans to set up a forward operational headquarters where it will be joined by Japan's Central Readiness Force.

The U.S. Navy and the Japan Maritime Self Defense Force have what an American officer calls "probably the strongest daily naval relationship in the world." Japan and the U.S. are developing a joint missile defense. All told, the U.S. expects to keep 42,000 military people in Japan after 8,000 Marines have been transferred to Guam.

In contrast, over the next five years the U.S. will draw down its forces in South Korea beyond the 29,500 level to be reached next year. The Combined Forces Command, a joint U.S.-Korean headquarters, will be dismantled. Most likely, the U.S. Eighth Army headquarters and that of the 2nd Infantry Division, whose troop level has already been cut, will be moved to the U.S.

In a realignment of U.S. forces, 30 bases have been returned to South Korea; another 29 will be returned later. Seoul plans to reduce its own forces by 45 percent over the next decade to 2 million troops. Despite U.S. requests, South Korea has resisted taking part in joint missile defense.

The conventional explanation of bad blood between Koreans and Japanese is the 35 years of harsh Japanese occupation of Korea from 1910 to 1945. The ill feelings, however, seem deeper and are not the same on either side. In its simplest generality, Koreans hate Japanese and Japanese disdain Koreans.

In March, for instance, Prime Minister Shinzo Abe of Japan said that Korean, Japanese, and other women who served as "comfort women," or sex slaves, for Japanese soldiers in World War II had done so for money. He brushed aside arguments that they were forced into it. "The fact is," Abe said, "there is no evidence to prove there was coercion."

Koreans exploded. A scholar, Kim Jin-hyun, reflected the sentiments of his compatriots in an essay in which he pointed to what he called "the uncivilized, historically fallacious, anti-humanitarian, and illogical displays by mainstream Japan."

Richard Halloran is a Honolulu-based journalist and former New York Times correspondent in Asia. His column appears weekly in Sunday's Focus section.