A proposed $18.2 billion purchase of U.S. weapons by Taiwan has bogged down in the island's hard-fought electoral politics despite repeated warnings from the Bush administration that the new arms are imperative to bolster defenses against China.

For some Taiwanese, controversy over the arms package has demonstrated the vitality of Taiwan's democracy, a noisy close to the era when generals could make such decisions behind closed doors. But in the view of Pentagon officials, the objections and politicking have sent the wrong message to Chinese leaders, who have vowed to use force if necessary to regain Taiwan and have arrayed 600 short-range ballistic missiles across the 100-mile Taiwan Strait to reinforce their threat.

Richard Lawless, the Pentagon's deputy undersecretary for Asian and Pacific affairs, told a Taiwan television network Tuesday that if the purchase of planes, missiles and submarines is not approved before the end of this year, there will be "serious repercussions" for the United States and Taiwan.

"It will be regarded as a signal, if you will, as the attitude of the legislature toward the national defense of Taiwan," Lawless said.

But government and opposition officials said resistance to the arms deal has swelled to the point where there is little chance it can be approved in the legislature, as required, before Taiwan's parliamentary elections, scheduled for Dec. 11. Moreover, the outcome of the vote will help determine whether President Chen Shui-bian's government can ever win approval for such a large purchase, they said.

Retired Adm. Nelson Ku, a leading figure in the opposition People First Party, said the arms package would have to be separated into its various components and renegotiated in order to be approved this year or next year. The Defense Ministry and other parts of Chen's administration have quietly started to scout for cheaper alternatives to U.S. submarines that, at about $12 billion, are the costliest part of the proposed sale, Ku and other officials said.

"If worse comes to worse, maybe there is another way," Foreign Minister Mark Chen said in an interview.

The delay and uncertainty have become a sore point for the Bush administration, which first approved $20 billion to $30 billion in arms sales to Taiwan in 2001. Since then, with growing frustration, Pentagon officials have been urging the island to come up with the money to make a purchase.

The Taiwan Relations Act, adopted in 1979 after Washington accorded diplomatic recognition to the government in Beijing, commits the United States to help Taiwan defend itself and to provide the self-governing island with adequate weaponry. In that context, the readiness of the government here to budget for military equipment -- enough to hold out against a Chinese attack until U.S. help could arrive -- has become a litmus test in Washington for U.S.-Taiwan military ties.

"How can we expect the Americans to support us if we are not willing to come to our own defense?" said Bikhim Hsiao, a legislator in President Chen's Democratic Progressive Party.

Chen, in a National Day message Sunday, portrayed the deal as a vital step toward maintaining peace in the Taiwan Strait that should rise above differences among the island's parties. "We should not allow interim political strife to compromise our nation's long-term security," he declared.

Chen's government, after the appointment of a new defense minister, decided in May to buy 12 P-3C Orion submarine-hunting aircraft, eight diesel-electric submarines and six PAC-3 (Patriot Advanced Capability-3) missile batteries with a complement of 350-plus missiles. Since then, it has lobbied hard to win support for the purchase, buying billboard space on Taipei buses, sending generals onto television talk shows and dispatching military song-and-dance troupes to provincial towns for national security musicals.

In a display of zeal that produced smiles around the island, Defense Ministry officials recently suggested the price could be borne if Taiwanese would, for a time, forgo drinking pearl milk tea, a local favorite in which flour is mixed into tea and milk, forming tapioca-like bubbles.

"It's expensive, but if we want to maintain peace, we have to make the other side understand we are not going to give up our security," Mark Chen, the foreign minister, said.

Zhang Ya Chung, a former diplomat who teaches at National Taiwan University, has organized a group called Democracy Action Alliance to promote opposing views. His followers staged a rally that drew more than 10,000 people in Taipei two weeks ago, and they have scheduled similar gatherings in other Taiwan cities to fight the sale.

"We think this big amount of weapons cannot protect Taiwan," Zhang said. "China is such a big country. How can Taiwan win an arms race with China?"

Public opinion polls have portrayed a divided picture, with government surveys showing a majority approving the purchase and opposition surveys showing a majority against it. Zhang and other opponents said the public had spoken by defeating a government-sponsored ballot initiative last March asking whether Taiwan should acquire more advanced weapons.

Few in Taiwan have suggested the island does not need at least some of the new arms. Its submarine fleet consists of two World War II Guppies and a pair of Dutch-made Zwaardvis-class craft acquired 16 years ago. By contrast, China could field more than 40 submarines around this 13,800-square-mile island, including quiet Kilo-class craft purchased from Russia and China's own Ming- and Song-class subs.

With the deployment of short-range ballistic missiles in southern China growing by about 75 a year, U.S. and Taiwanese officials here have argued, the need for PAC-3 antimissile systems is obvious. And they said the Orion submarine hunters would be necessary in any conflict to defend against China's growing underwater fleet.

"We are losing our qualitative edge," said Joseph Wu, who heads Chen's key Mainland Affairs Council. But the issue at hand is whether the deal pushed by the Bush administration and adopted by the Chen government is a wise balance of Taiwan's defense needs and its economic resources, opponents said.

"We are not against the military sale, but we have to think about whether we can afford it," said James Song, who heads the People First Party, which is allied with the main opposition group, the Nationalist Party. In an interview, he added: "We must do good shopping. We must get what is best for us."

The Nationalists, who were in power when discussions began on the arms sales during the Clinton administration, so far have maintained an ambiguous position, criticizing Chen's deal but not saying clearly how the party will vote. Political figures said the outcome of voting in December would help shape the Nationalists' stand.

The current legislature will return in late December for a final sitting. By then, the makeup of the newly elected Taiwanese legislature will be known. If Chen's party has a majority in the next legislature, which begins in March, the new atmosphere could favor the government, Bikhim and other politicians suggested. "We are not going to just give up if this doesn't pass now," Bikhim said in an interview.

But the post-election situation is far from clear, other analysts cautioned, and passage of the arms budget as it now stands is not guaranteed even if Chen's party is victorious in December.

Special correspondent Tim Culpan contributed to this report.

A couple in Beijing walks by a billboard of a Chinese warship firing a missile. The U.S. wants Taiwan wants to buy arms to maintain a balance of power. The government of President Chen Shui-bian decided in May to buy arms from the U.S. Since then, it has lobbied to gain support for the deal.