THE love-hate relationship between the United States and China is always difficult, but it seems to have entered a phase when it is touchier than usual. A number of issues of late have soured relations between the two giant nations: China's expulsion of activist Han Dongfang; conflict over China's textile exports; America's efforts to control the trade in non-conventional weapons; and, now, reports that the US is to sell highly potent Harpoon missiles to Taiwan. America has pushed hard on the questions of human rights and arms control and China has decided to push back hard - and angrily. China gives the impression of not caring about international opinion, Olympics bid or no Olympics bid. Certainly, it went on the offensive to defend the indefensible, when it justified its expulsion of one of its own citizens. That action was outside the norms of international law; it is akin to feudal notions of exile as a way to handle those who cause the authorities difficulty. But China is on stronger ground when it complains about American pressure on various forms of the arms trade. The United States imposed economic sanctions on China for sending M-11 missile parts and technology to Pakistan, supposedly in breach of the Missile Technology Control Regime, an international pact which China has not signed but has pledged to honour. As this newspaper has noted before, the Americans have failed to produce evidence that any breach of the agreement occurred. And China has a right to be furious with the US over the Yinhe incident. The Yinhe, a Chinese ship trading in the Middle East, was shadowed by the US Navy for three weeks, and denied entry to a number of ports, because the United States had decided it was carrying chemicals used in making chemical weapons. It was allowed to put in to the port of Dammam, in Saudi Arabia, so it could be inspected. The inspectors found no trace of the chemicals. US intelligence, it seems, was wrong. China has demanded an apology and financial compensation. At the very least, it should expect the former. All it has received, however, is a grudging comment from the State Department to the effect that the incident was unfortunate. The United States must be embarrassed by its own mistake but that is no good reason for being so mean-spirited. Both China and the US have much to gain - economically, politically and culturally - from good and close relations. Their relationship is important internationally, as well - in promoting greater prosperity and stability. Securing a smooth relationship should be a prime goal of both countries' foreign policies. It is not the only goal, of course. American political leaders are right to put pressure on China to improve its human rights performance. But they have to be careful not to let their enthusiasm lead them into errors and false accusations. It damages US credibility on a critical issue. And it adds needless irritation to a critical, but troublesome, relationship.