Mr. Chen on Tuesday completed the formalities for scrapping the National Unification Council and guidelines for unification with mainland China. Though largely moribund, the council and the guidelines were symbols of Taiwan's political links to Beijing that Mr. Chen had once vowed to preserve.
Mr. Hu said the move threatened stability in the Taiwan Strait and the region.
"We will continue to strive for the prospect of peaceful reunification, but never tolerate the secession of Taiwan from the motherland," Mr. Hu said in remarks published by the official New China News Agency.
The Taiwanese government rejected the mainland's objections, repeating Mr. Chen's position that Taiwan was trying only to preserve a balance in its relations across the Taiwan Strait as China builds up its military forces facing the island.
"The criticism by China is groundless," said Joseph Wu, the chairman of the Mainland Affairs Council, the Taiwan government agency that handles relations with Beijing. "What we are doing has nothing to do with changing the status quo."
But experts in China said the action had shaken Beijing's confidence that Mr. Chen's recent electoral setbacks and pressure from Washington would check his drive for formal independence. Beijing had hoped that the upset victory of the opposition Nationalist Party in local elections last year had stymied Taiwan's independence movement.
And many Chinese foreign policy experts expected that the Bush administration would do more than it had done to prevent Mr. Chen from trying to legalize Taiwan's de facto independence.
"The reality is that even under heavy American pressure, Chen Shui-bian is determined to provoke a big response from China," said Huang Jiashu, a Taiwan expert at People's University in Beijing.
"He pushes through this measure today and something else tomorrow," Mr. Huang said, adding that "you cannot rule out a confrontation before 2008," when Mr. Chen's second and final term ends.
Mr. Chen still faces an uphill struggle to achieve formal independence for Taiwan, the main goal of his core political constituency. His approval ratings have sunk below 30 percent in some recent polls. The Taiwan legislature, which would have to approve changes to the island's constitution, is controlled by the Nationalists, who favor more cordial ties with the mainland.
Moreover, the United States, Taiwan's only major military and political partner, has tried to check creeping moves toward independence. Washington needs China's help in managing pressing problems like the nuclear programs in North Korea and Iran, and seems determined to prevent Taiwan from undermining diplomatic ties to Beijing.
Even so, the scrapping of the unification council, which Mr. Chen first signaled in late January, was widely viewed in Beijing as a test of how successfully the United States could constrain Mr. Chen.
After a concerted diplomatic push by the Bush administration, Mr. Chen modified the wording of his order, saying the council would "cease to function" rather than be abolished, the term he had used in January. He also reiterated his pledge to maintain the status quo in cross-strait relations.
The pledge and the wording change appeared to reassure Washington. The State Department issued a statement on Monday noting Mr. Chen's decision not to abolish the council formally, suggesting that Washington considered that a significant concession.
But in Beijing's view, Mr. Chen effectively prevailed over Washington's objections.
"Although he did not use the term 'abolish' and changed the term to 'cease function,' this is merely a word game," China's Taiwan Affairs Office said. "Basically he is tricking the Taiwan people and international opinion."
Yan Xuetong, an international relations expert at Tsinghua University in Beijing, said Mr. Chen had shown that he could manage American pressure. Though Mr. Chen violated his onetime pledge to the United States to leave the unification council in place, he ended up winning tacit American support for his effort to terminate it, Mr. Yan said.
Mr. Huang of People's University gave the United States credit for forcing at least a nominal concession from Mr. Chen, but said China would probably look for President Bush to make a fresh commitment to oppose Taiwanese independence, perhaps during the planned visit of President Hu to Washington in April.
In Taiwan, some lawmakers argued that Mr. Chen's move was vital to preserving a balance in cross-strait relations. Hsiao Bi-khim, an influential lawmaker from Mr. Chen's governing Democratic Progressive Party, said Mr. Chen had been increasingly worried that China had been trying to gain the upper hand.
"He feels that you need to do something drastic to pull things back into balance," she said, adding that she did not expect any further initiatives on sovereignty issues..