Leading article: A nervous encounter that portends future rivalry

Superpower summitry is a concept that declined and fell with the Soviet Union. For the best part of 15 years, the very idea that two leaders meeting in one place might briefly hold the fate of the world in their hands has seemed long out of date; the austere mystique that attended such occasions was forgotten. The wary encounter that begins in Washington tomorrow, however, suggests that superpower summitry may be on its way back.

The President of China, Hu Jintao, is banishing his jet lag by stopping over in Seattle to see Microsoft and Boeing. The pause is an opportunity for Washington too: to impress. China, for all its rapid economic growth, has nothing to rival either of these two global companies. Mr Hu is intended to arrive at the White House with a due appreciation of US economic might.

As the preliminaries indicate, this will not be an easy summit. It occupies uncomfortable protocol territory, short of a full state visit, but with more ceremonial than a routine official visit. President George Bush needs to respect the dignity of his visitor, but not to excess. The immediate items on the bilateral agenda are not, for the most part, to the US advantage.

On the most urgent issue, the $200bn trade deficit that the US has built up with China, Mr Bush comes to this summit as a supplicant. Washington has been exerting pressure on China to revalue its currency for at least two years now, with precious little to show for its trouble. Imports from China keep rising, and the deficit along with them. Cheap manufactured goods keep the US inflation rate down and American consumers happy - but they are not good for the US bottom line.

Mr Bush has not been the most vocal US critic of China's currency policy; he has not needed to be. Others have been only too willing to do the job for him. But he may also appreciate the contradiction. The US cannot fast-track China into the World Trade Organisation and preach the undoubted virtues of the free market, while at the same time trying to set China's national currency policy. Currency policy is for Beijing to decide in its own national interest.

On the other hand, the levers that the United States does have at its disposal, it has declined to use. The outrage that Mr Bush and his Secretary of State, Condoleezza Rice, routinely express about limitations on human rights and free expression elsewhere is almost never invoked against China, despite pervasive censorship - including of the internet, in which US companies have been complicit. Hopes that President Hu might preside over political relaxation have so far not been realised. A little naming and shaming could have a salutary effect on a country which has so highly developed a sense of its own importance and increasingly aspires to cut a figure abroad.

In the greater sweep of history, however, trade and human rights may well come to seem short-term irritations compared with the rivalry of truly superpower proportions that surely looms on the horizon. Sections of the US Congress have sensed danger for a decade. The anti-missile defence programme is driven by fear of more than just North Korea's nuclear capability. The status of Taiwan is not only a relic of a past conflict, but a potential spark for a new one. As the US belatedly courts India, China is extending its influence not only into its traditional trading zones in South-east Asia, but into Africa as well. Its thirsty economy is seeking oil from the Gulf.

This week's Bush-Hu meetings may not qualify as a fully-fledged superpower summit. Give the US and China another decade, though, and the world might well need to hold its breath when their two leaders meet.