On Wisconsin Avenue in Washington DC is an imposing modern building, home to the Taipei Economic and Cultural Representative Office.

A casual observer might mistake it for a Taiwanese embassy, which to all intents and purposes is what it is, apart from the fact that Taiwan, in the eyes of the United States, is part of China.

The relationship between the superpower and the Chinese island is an ambiguous one, and Washington prefers to keep it that way.

Economic allies

The ambiguity began on 1 January 1979 when, after having recognised the government in Taipei for three decades, Washington finally accepted that the Communists in Beijing were the sole legal authority in China, and Taiwan was part of that country.

President Nixon's 1972 visit to China changed US relations with Taiwan

At the same time the US made clear that it would continue to have cultural, commercial, and other unofficial relations with Taiwan, as enshrined in the Taiwan Relations Act signed by President Jimmy Carter later that year.

The mutual defence pact with Taiwan was ended, but Washington has reserved the right to sell defence equipment to Taiwan, arguing that the peace and stability of the region is in the US national interest.

Certainly, Taiwan's economic progress has been in both countries' interest.

The island of some 22 million people is the world's 12th largest economy, and America's seventh-largest trading partner. In 1998 two-way trade totalled about $51bn and that's only likely to rise.

One measure of the island's importance to the US is that when computer chip production in Taiwan was disrupted by last year's earthquake, computer prices rose across America.

Democracy

But the US commitment to Taiwan is not just about economics.

It is also driven by the defence of democracy, historical resistance to the spread of communism, and a desire to keep sending a message to the people on the mainland.

The US wants to show the Chinese people on the mainland that a little way offshore, their countrymen are thriving because they have shed the communist system and embraced democratic government.

Arms to Taiwan

An E-2T early warning aircraft Equipment for F-16 and other military aircraft Hellfire air-to-surface missiles Knox-class destroyers Chinook helicopters Chaparral missiles M-46 torpedoes Harpoon anti-ship missiles

For all these reasons, the US has been a staunch protector of Taiwan.

When China fired missiles into the Taiwan Straits in the run-up to the island's first presidential elections in March 1996, the US sent two aircraft carrier battle-groups to the region.

It was the biggest show of US naval force in the region since the Vietnam War.

The US has also armed Taiwan so comprehensively that most analysts agree China would not be able to mount a successful invasion.

Diplomatic minefield

These arms sales are a major part of the diplomatic minefield that Washington has to navigate with Beijing.

President Clinton says the US still holds to the "one China" principle

Washington knows that relations with China are already strained over American support for the independence of Taiwan, if not for Taiwanese Independence.

To maintain relations with Beijing, the US is forced to navigate cautiously and work to prevent anyone rocking the boat.

In the aftermath of the March '96 confrontation, President Bill Clinton, re-affirmed that the US still has a "one China" policy and does not support Taiwanese independence, or Taiwanese membership of organisations that require statehood.

Hence US officials were furious in July last year, when Taiwan's then President Lee Teng-hui declared that relations with Beijing should be on a "state-to-state" basis.

Bellicose language

Taiwan's new president Chen Shui-bian can expect little support from Washington if he chooses to push the point.

The US says it will act if China uses force against Taiwan

But Washington was equally critical of bellicose language used by China earlier this year in which it stated formally for the first time, that China would use force against Taiwan if it delayed re-unification talks indefinitely.

Some China-watchers dismissed such talk as mere bluster aimed at Taiwan's voters as they prepared to choose a new president - better a rhetorical salvo, they said, than more missiles.

But the Clinton administration took the threat seriously. White House spokesman Joe Lockhart indicated the US would be prepared to act again if Beijing stepped up its military threat.

Ready for war?

So the big question is whether the US would actually be prepared to go to war with China over Taiwan.

The US points to its military build-up in the region four years ago as proof of its commitment.

But deploying battleships, and actually firing on China are very different things, and President Clinton has gone to great lengths to improve relations with Beijing which he would not throw away lightly.