BEIJING, Feb. 21 –– China warned today it will use military force against Taiwan if the island's leaders indefinitely delay negotiations on reunification with the mainland, adding a new element of tension to East Asia's most volatile standoff.

The ultimatum significantly broadened China's long-standing threat to invade the island under certain conditions. China previously had said it would take Taiwan by force if it declares independence or is occupied by a foreign power. Now an unspecified delay in reunification talks
has been added to the list.

The warning was issued in an official white paper from the State Council, the highest organ of China's government. One of an irregular series of policy statements, it came just one month before presidential elections in Taiwan, which split off from China after the 1949 civil war that brought Mao Zedong and the Communist Party to power.

"If the Taiwan authorities refuse . . . the peaceful settlement of cross-straits reunification through negotiations, then the Chinese government will only be forced to adopt all drastic measures possible, including use of force," the paper said.

At the same time it issued the warning, the white paper appeared to agree to one of Taiwan's main conditions for political talks with Beijing--that Taiwan be treated as an equal and not as a local government. This has been an important sticking point, with China insisting Taiwan is a renegade province and the island's leaders demanding recognition of their half-century of separate government.

But the paper rejected outright a key second condition put forth by the Taiwanese government for talks to begin: political reform in China.

The paper also suggested China would be justified in attacking Taiwan if the United States continues arms sales to the island, whose political system is becoming more democratic, or if Taiwan revises its constitution to modify support of the "one China" principle--the idea that, even though Beijing and Taipei have separate governments, there is only one China.

U.S. officials in Washington said the State Department is studying the lengthy document carefully, particularly the section saying China has added a new criterion for deciding on an invasion, but will refrain from detailed reaction until the full meaning is clear.

"We have an abiding interest in peaceful resolution of the cross-strait issue," State Department spokesman James P. Rubin said. "And we urge both sides to foster dialogue to resolve that issue."

The new warnings from Beijing seemed likely to increase support in the U.S. Congress for the Taiwan Security Enhancement Act, which calls for increased communication between the U.S. and Taiwanese armed forces, and for suggestions by some lawmakers that the United States endow Taiwan with a missile defense system.
 China's ultimatum, embedded in the lengthy white paper, seemed timed to affect the outcome of Taiwan's presidential elections, scheduled for March 18 to replace President Lee Teng-hui.

Chen Shui-bian, the candidate from the opposition Democratic Progressive Party, has in the past advocated independence for Taiwan. Chen is running neck-and-neck with two other main candidates, Vice President Lien Chan and independent James Soong, who both back closer ties to China. Beijing is believed to prefer Lien.

All three candidates have said Taiwan is a sovereign state separate from Beijing. They all have generally rejected the concept of "one China," even though that idea is enshrined in Taiwan's constitution.

The paper came at a time when most analysts believe relations are set to improve following a tense period last summer when Lee announced he was rejecting the "one China" policy that has been the bedrock of ties since relations began to thaw in the late 1980s. Lee said that Taiwan and China are separate countries and should establish "special state-to-state relations," infuriating Beijing.

"The good news is that this is better than something military," said Michel Oksenberg, an expert on China's security affairs at Stanford University. "The bad news is that the Chinese felt compelled to do anything at all when it looked liked things were heading their way."

Following the return of Hong Kong and Macau to Chinese control, the white paper is a sign of Beijing's growing impatience with the pace of reunification with Taiwan and indicates specifically that China's military has increased influence over President Jiang Zemin in the formation of policy toward the island. The military is known to be more willing to embrace a violent solution to the issue and is engaged in a multibillion-dollar modernization drive focused almost completely on "liberating Taiwan."

But the ultimatum also underscores China's failure to devise policies to entice Taiwan into building on the positive side of the relationship. Indirect trade between the two sides has reached $160 billion, Taiwanese companies have invested $44 billion in China, 200,000 Taiwanese live in mainland China and 16 million Taiwanese have traveled to China since relations began thawing in 1987.

The language in the white paper seemed to harken back to 1996, the year of Taiwan's first direct presidential election, when China carried out war games in the Taiwan Strait weeks before the vote. Those war games prompted the United States to dispatch two aircraft carrier battle groups to the region and contributed to a sweeping victory by Lee--the opposite of what China wanted.
Chinese civilian officials acknowledge privately that policy backfired, but the People's Liberation Army is known to think that it succeeded.

But it is significant, said Oksenberg, that words, not missiles, are flying across the 100-mile wide Taiwan Strait. The white paper appeared to be a tactical maneuver, he added. "The two sides are circling around each other to see about resumption of dialogue after the election," he said. "They are trying to set the terms of the debate."