HANOI, Vietnam — With tensions between China and Japan spilling out at an East Asian summit meeting here, the United States is trying to defuse an escalating diplomatic row over their competing claims to a cluster of small islands in the East China Sea.

On Saturday, Secretary of State Hillary Rodham Clinton proposed a three-way meeting with China and Japan to resolve the dispute, which has raged since last month when Japan detained the captain of a Chinese fishing vessel that struck two Japanese patrol boats near the islands.

"We have certainly encouraged both Japan and China to seek peaceful resolution of any disagreements that they have," Mrs. Clinton said at a news conference after the summit meeting ended. "It is in all of our interest for China and Japan to have stable, peaceful relations."

In private conversations with Chinese and Japanese diplomats, Mrs. Clinton "made very clear to both sides that we want the temperature to go down on these issues," a senior official said. American officials said they were troubled by what one called a sudden, drastic increase in tensions.

As the United States, Russia and 16 Asian nations gathered in Hanoi to discuss regional cooperation, China's aggressive maritime and territorial claims were sowing unease with several of its neighbors.

When Japan last week reasserted its sovereignty over the islands — which it calls the Senkaku and China calls the Diaoyu — a senior Chinese official accused it of ruining the atmosphere of the summit meeting.

The United States, which had been mostly a bystander in such disputes, has taken a more active role under the Obama administration. Though it has no position on the sovereignty claims, Mrs. Clinton said the United States viewed the islands as protected under the terms of its defense treaty with Japan, which means it will defend them from any foreign attack.

That statement brought a rebuke from the Chinese Foreign Ministry spokesman, Ma Zhaoxu, who said China "will never accept any word or deed that includes the Diaoyu Islands within the scope" of the treaty.

On another issue that has caused friction lately — China's halting of shipments of strategically important minerals to the United States, Japan and Europe — the Chinese government seemed eager to reassure.

In a meeting with Mrs. Clinton, Foreign Minister Yang Jiechi gave "very clear indications" that China would fulfill its contracts and be a "reliable supplier," according to an American official.

"While we're pleased by the clarification received from the Chinese government," Mrs. Clinton said, "we still think the world as a whole needs to find alternatives" to China as a supplier of the minerals, known as rare earth metals.

China began curtailing shipments to the United States and Europe of these minerals, which are used to make products like cellphones and wind turbines, after the dispute with Japan and a trade investigation by the Obama administration. Then last week, without explanation, Chinese officials said the shipments would resume.

Japan, which released the Chinese captain under heavy pressure from Beijing, had proposed a meeting with Chinese leaders in Hanoi to clear the air. But hopes for that were dashed when Japan's foreign minister, Seiji Maehara, asserted Japan's control over the islands last week.

Prime Minister Wen Jiabao of China refused to meet one-on-one with Prime MinisterNaoto Kan of Japan, though Mr. Yang said China would consider Mrs. Clinton's proposed trilateral meeting.

In her formal remarks to the Asian leaders, Mrs. Clinton reiterated that the United States stood ready to help resolve another territorial dispute: one that pits China against Vietnam, the Philippines and other countries over a string of strategically significant islands in the South China Sea.

"The United States has a national interest in the freedom of navigation and unimpeded lawful commerce," she said. "And when disputes arise over maritime territory, we are committed to resolving them peacefully based on customary international law."

The administration's position angers China, which has also sparred with the United States over currency policy and trade. Chinese officials have expressed concern that all the friction could get in the way of a visit to the United States early next year by President Hu Jintao.

At Beijing's request, Mrs. Clinton added a last-minute China stop to her itinerary, meeting the state councilor for foreign affairs, Dai Bingguo, on Saturday on Hainan Island, east of Vietnam. She pressed Mr. Dai to use Beijing's influence on North Korea to discourage it from "provocative" acts before the Group of 20 leaders' meeting in Seoul next month.