WASHINGTON » The Obama administration, facing a vexing relationship with China on exchange rates, trade and security issues, is stiffening its approach toward Beijing, seeking allies to confront a newly assertive power that officials now say has little intention of working with the United States.

In a shift from its assiduous one-on-one courtship of Beijing, the administration is trying to line up coalitions — among China’s next-door neighbors and far-flung trading partners — to present Chinese leaders with a unified front on thorny issues like the currency and their country’s territorial claims in the South China Sea.

The advantages and limitations of this new approach were on display during the weekend at a meeting of the world’s largest economies in South Korea. The United States won support for a concrete pledge to reduce trade imbalances, a stance that will put more pressure on China to allow its currency to rise in value.

But Germany, Italy and Russia balked at a U.S. proposal to place numerical limits on these imbalances, a step that would have further isolated Beijing. That left the Treasury secretary, Timothy F. Geithner, to make an unscheduled stop in China on his way home from South Korea to discuss the deepening tensions over exchange rates with a top Chinese finance official.

Administration officials speak of an alarming loss of trust and confidence between China and the United States over the past two years, forcing them to scale back hopes of working with the Chinese on major challenges like climate change, nuclear nonproliferation and a new global economic order.

The latest source of tension is over reports that China is withholding shipments of rare-earth minerals, which the United States uses to make advanced equipment like guided missiles. Administration officials, clearly worried, said they did not know whether Beijing’s motivation was strategic or economic.

"This administration came in with one dominant idea: make China a global partner in facing global challenges," said David Shambaugh, director of the China policy program at George Washington University. "China failed to step up and play that role. Now, they realize they’re dealing with an increasingly narrow-minded, self-interested, truculent, hyper-nationalist and powerful country."

To counter what some officials view as a surge of Chinese triumphalism, the United States is reinvigorating cold war alliances with Japan and South Korea and shoring up its presence elsewhere in Asia. This week, Secretary of State Hillary Rodham Clinton will visit Vietnam for the second time in four months, to attend an East Asian summit meeting likely to be dominated by the China questions.

Next month, President Barack Obama plans to tour four major Asian democracies — Japan, Indonesia, India and South Korea — while bypassing China. The itinerary is not meant as a snub: Obama has already been to Beijing once, and his visit to Indonesia has long been delayed. But the symbolism is not lost on administration officials.

Jeffrey A. Bader, a major China policy adviser in the White House, said China’s muscle-flexing became especially noticeable after the 2008 economic crisis, in part because Beijing’s faster rebound led to a "widespread judgment that the U.S. was a declining power and that China was a rising power."

But the administration, he said, is determined "to effectively counteract that impression by renewing American leadership."

Political factors at home have contributed to the administration’s tougher posture. With the U.S. economy sputtering and unemployment high, Beijing has become an all-purpose target. In this congressional election season, candidates in at least 30 races are characterizing China as a threat to U.S. jobs.

At a time of partisan paralysis in Congress, anger over China’s currency has been one of the few areas of bipartisan agreement, culminating in the House’s overwhelming vote in September to threaten China with tariffs on its exports if Beijing did not let its currency, the renminbi, appreciate.

The trouble is that China’s own domestic forces may cause it to dig in its heels. With the Communist Party embarking on a transfer of leadership from President Hu Jintao to his anointed successor, Xi Jinping, the leadership is wary of changes that could hobble China’s growth.

There are also increasingly sharp divisions between China’s civilian leaders and elements of the People’s Liberation Army. Many Chinese military officers are openly hostile toward the United States, convinced that its recent naval exercises in the Yellow Sea amount to a policy of encircling China.

Even the administration’s efforts to collaborate with China on climate change and nonproliferation are viewed with suspicion by some in Beijing.

Obama’s aides, many of them veterans of the Clinton years, understand that especially on economic issues, there are elements of brinkmanship in the relationship, which can imply more acrimony than actually exists.

But the White House was concerned enough that last month it sent a high-level delegation to Beijing that included Bader; Lawrence H. Summers, the departing director of the National Economic Council; and Thomas E. Donilon, who has since been named national security adviser.

"We were struck by the seriousness with which they shared our commitment to managing differences and recognizing that our two countries were going to have a very large effect on the global economy," Summers said.

Just before the meeting, China began allowing the renminbi to rise at a somewhat faster rate, although its total appreciation, since Beijing announced in June that it would loosen exchange-rate controls, still amounts to less than 3 percent. Economists estimate that the currency is undervalued by at least 20 percent.

Meanwhile, trade tensions between the two sides are flaring anew. The administration recently agreed to investigate charges by the United Steelworkers that China was violating trade laws with its state support of clean-energy technologies. That prompted China’s top energy official, Zhang Guobao, to accuse the administration of trying to win votes — a barb that angered White House officials.

Of the halt in shipments of rare-earth minerals, Summers said, "There are serious questions, both in the economic and in the strategy realm, that are going to require close study within our government."

Beijing had earlier withheld these shipments to Japan, after a spat over a Chinese fishing vessel that collided with Japanese patrol boats near disputed islands. It was one of several recent provocative moves by Beijing toward its neighbors — including one that prompted the administration to enter the fray.

In Hanoi in July, Clinton said the United States would help facilitate talks between Beijing and its neighbors over disputed islands in the South China Sea. Chinese officials were livid when it became clear that the United States had lined up 12 countries behind the U.S. position.

With Hu set to visit Washington early next year, administration officials said Clinton would strike a more harmonious note in Asia this week. For now, they said, the United States feels it has made its point.

"The signal to Beijing ought to be clear," Shambaugh said. "The U.S. has other closer, deeper friends in the region."

© 2010 The New York Times Company