SEOUL » The sighs of relief in Washington have almost been audible. As the United States forges ahead with efforts to counter China’s influence in Asia, Japan and South Korea this week both elected conservative, pro-U.S. leaders, raising hopes that the U.S. and its two closest Asian allies can work together on the vexing security issues roiling this economically vibrant region.

All those issues, that is, except one: Tokyo and Seoul’s emotionally charged relations with each other, which show no signs of easing under right-wing, nationalistic governments in power.

The tensions between its two closest partners in the region have already proven a headache for the U.S., which has been pressing the two export powerhouses to take a bigger role in regional security to ease its own budgetary pressures. But the neighbors remain hamstrung by history, and even a relatively small deal on intelligence sharing unraveled this summer amid a dispute over how to view Japan’s harsh colonization of the Korean Peninsula before World War II.

"The U.S. might think it’s great to have two conservative governments, but these are two allies that can’t even sign a minor agreement," said Daniel C. Sneider, a researcher on East Asian diplomacy at Stanford University.

The question, then, is whether the U.S. can effectively deal with China’s rise if the allies, who host some 75,000 U.S. troops and sailors, find it so hard to work with each other.

Even with those worries, the elections were seen as a win for Washington as it struggles to contain a nuclear-armed North Korea and counter China’s military buildup.

In both elections, the winners defeated opponents who raised at least some alarms in Washington.

In Japan, a blowout victory by the Liberal Democrats on Sunday ensured the prime ministership will go to Shinzo Abe, a nationalist who has vowed to restore close military cooperation with the United States that frayed under a left-leaning government during a dispute over an U.S. base. One of the losers was a party led by Shintaro Ishihara, known for railing against his nation’s servility to the U.S. and for provoking a territorial spat with China that the U.S. fears being dragged into.

In South Korea, Park Geun-hye won on Wednesday with promises to keep the close bonds that the incumbent, Lee Myung-bak, cultivated with the Obama administration, a relationship that analysts in both countries say is the best ever by leaders of the two nations. Park defeated a liberal candidate who wanted an immediate restart of extensive aid to North Korea that some feared would undermine U.S.-led sanctions against the North’s nuclear program.

The Obama administration quickly embraced both victors. After a phone call with Obama, Abe announced that he would go to Washington in January for the first visit abroad as prime minister, and Park’s aides said her first presidential visit abroad would also most likely be to the U.S.

The new leadership is a particular relief for the United States after a decade in which both countries have sometimes bridled at Washington’s hold on them, with public sentiment seeming to veer at times between viewing the large U.S. military as a welcome protection and an affront to national dignity.

The U.S. has benefited from China’s increasingly sharp-elbowed approach to its neighbors, especially Japan, with whom it is locked in an increasingly shrill dispute over islands in the East China Sea.

"In both Japan and South Korea, the perception of China has changed to being a threat, and that has made the U.S. seem much more favorable as a source of security," said Narushige Michishita, a security affairs expert at the National Graduate Institute for Policy Studies in Tokyo.

While South Korea has less direct tension with China, Korean experts said that Chinese support of Pyongyang, even after the 2010 sinking of a South Korean warship that the South blamed on the North and a deadly rocket attack that year on a South Korean island, has fueled a pro-U.S. mood that may have played a role in Park’s election.

Abe has promised to reinterpret his nation’s anti-war constitution to allow Japan’s military, seen as the most technologically advanced in Asia, to aid U.S. forces in combat. The U.S. has also welcomed Abe’s calls to expand security ties with other democracies in the region, like Australia and India, as a way to offset China’s growing presence. But analysts say Japan will need to reverse a decline in military spending before Washington is convinced Tokyo is doing enough to keep China’s aspirations in check.

The U.S. is also asking South Korea to use its superior economic and technological power to help it shoulder more of its own defense against a possible attack from the heavily armed North. Washington wants a reliable ally in 2015, when it plans to transfer command of its own and South Korean troops on the peninsula to Seoul during a crisis.

While Park has said she will reach out to China, she says improved ties with Beijing are not a zero-sum game with Washington, with whom South Korea will remain a close ally.

"With Park and Abe, conservatives in both Seoul and Tokyo, Washington seems to have a coalition of the willing," Michishita said. "But it might have more difficulty than it imagines in finding any benefits."

There had been hopes that tensions might ease after Lee leaves office, but one side effect of installing two conservative governments might be to ensure that neither side is willing to give in on issues closely bound to national identity and pride, like the continuing fracas over Korean women forced into sexual slavery by Japan during World War II.

"South Korean-Japan ties are already in trouble, and there is probably only more trouble ahead with Abe and Park," said Hwang Ji-hwan, a professor of international relations at Seoul University.

The last time he was prime minister, in 2006-07, Abe drew criticism in Seoul and in the U.S. Congress for denying the position of the South Korean government and most historians that the women were coerced, saying they instead were common prostitutes. Park, a lawmaker at the time, went to Washington to attend congressional hearings that criticized Abe’s denials. During the presidential campaign, she shed her usual quiet reserve when she appeared to lecture a reporter for a conservative Japanese newspaper who asked about the worsening of Japanese-Korean relations.

"There is something that I really want to tell you," she said, emphasizing each word. The sex slave issue "cannot be justified in any way whatsoever." "I hope the wise leaders of Japan will deeply ponder this point."

Officials for all three nations say some efforts to soothe relations are already under way. Japanese and U.S. officials said that in November, the U.S. assistant secretary of state for Asian affairs, Kurt Campbell, privately urged Abe to shelve calls to revise a 1993 official apology to the women by Japan’s government.

For now, it appears that Abe got the message. Since his party’s victory, he has been carefully vague in his public comments on the women and whether he will visit a Tokyo war shrine, another emotional issue in South Korea. "Both sides have learned there is a line that you don’t want to cross," said Lee Chung-min, an adviser on international affairs to Park.

© 2012 The New York Times Company