U.S. national security adviser Condoleezza Rice met top Chinese leaders Thursday and rebuffed their demands for an end to U.S. arms sales to Taiwan, a senior U.S. official said. But Rice also told them the Bush administration was willing to help establish a dialogue between Beijing and the self-governing island.

The official, who is traveling with Rice and spoke on condition of anonymity, said Rice was not specific in the offer and told Chinese leaders only that the United States could take steps "to further dialogue if it's helpful."

In the past, the United States has rejected suggestions that it assume a mediator's role in the sensitive dispute between mainland China and Taiwan. But it has repeatedly urged both sides to open talks and settle their differences peacefully. In recent months, U.S. officials have expressed concern about rising tensions across the Taiwan Strait and the risk of U.S. forces being dragged into a conflict there.

The dispute over Taiwan dominated Rice's meetings on the first day of a two-day visit to Beijing. She met with Jiang Zemin, China's military chief and former president, and Foreign Minister Li Zhaoxing and was scheduled to see President Hu Jintao and another senior foreign policy official, Tang Jiaxuan, on Friday.

China claims sovereignty over Taiwan and has threatened to seize it by force if necessary, but Taiwan's newly reelected president, Chen Shui-bian, says the island is an independent country. The Chinese military is planning large-scale exercises this month involving joint sea, land and air operations on an island about 150 miles from Taiwan.

Jiang told Rice that the Chinese people are "seriously concerned and dissatisfied about a series of recent U.S. moves on the Taiwan issue, especially sales of advanced weapons to Taiwan," state media reported.

Rice's visit, her first to China since she accompanied President Bush here in 2002, comes during what appears to be an intensifying leadership struggle between Jiang and Hu, which is complicating the ruling Communist Party's decision-making on Taiwan and other issues. Chinese officials have said Jiang was resisting pressure to retire and has taken a hard-line position toward Taiwan to strengthen his grip on power.

In a possible setback for Hu, the party leadership has reportedly scheduled a round of informal meetings at the seaside resort of Beidaihe this month. For years, the party traditionally held the secretive gatherings every summer, but Hu canceled them soon after taking office last year in a move many analysts saw as an attempt to set a different tone for his new government.

The party has not announced if its leaders will be returning to Beidaihe this summer, but Chinese officials have said as much both to U.S. officials and to Hong Kong media organizations that have close ties to Beijing.

The senior U.S. official said Rice wanted to make sure that, going into those meetings, the Chinese leadership was clear on the Bush administration's commitment to strong relations with China, despite differences on Taiwan and other issues, including human rights and trade.

The official said Rice reaffirmed the U.S. position that it did not support independence for Taiwan and opposed unilateral action by either side to change the status quo.

She also urged the Chinese to put pressure on North Korea to accept a U.S. proposal to dismantle its nuclear weapons program in exchange for fuel and other benefits. The Chinese described the U.S. proposal as positive, claimed credit for the North Koreans not rejecting it and suggested that "a breakthrough" might be possible in September, at the next round of six-nation talks on North Korea's nuclear program, the U.S. official said.

Rice also pressed the Chinese to improve their record on human rights, and raised the cases of several political prisoners, including Jiang Yanyong, the elderly physician who exposed the government's cover-up of the SARS outbreak last year.

U.S. national security adviser Condoleezza Rice, left, shares a laugh with China's military chief and former president Jiang Zemin.