ONE of the Government's most fervent aims is to keep the Sino-British row out of the United States' imminent decision on renewal of China's Most Favoured Nation (MFN) trade status. But the trouble with rows is that they seldom oblige by staying in pigeon holes. Opponents will sweep up every bit of ammunition they can find, and as in every such war there is no such thing as playing fair. Already Mr and Mrs America are being dished up with a morning diet of corn flakes and news of Britain's push for democracy (democracy equals good) and China's increasingly disturbing rhetoric rejecting democracy (bad). Next month, when the champion of that democracy, Mr Chris Patten, charges into Washington, media interest in that city is bound to intensify. The man has already become a chat show hero - a thing for which the American appetite knows no bounds - and it can be tough to ignore a good drama, especially when the subject is as emotional as democracy and when one of the key protagonists is in town. This in turn must surely make it hard for America to remain on the sidelines. Speaking in Hongkong yesterday, US Sinologist Robert Sutter said the high-profile crisis which the row was rapidly becoming was increasingly likely to get tangled up into the debate on China policy. He said: ''Mr Patten has been getting a lot of publicity: he has been on Larry King, and there's David Frost. Now he is coming to the US and policy-makers are going to be asked to comment on the Hongkong situation, and are going to have to say something. ''It is natural for Americans to associate with Mr Patten against China. It is a David and Goliath situation, where Mr Patten is David and China is Goliath.'' But this is very possibly just the sort of support Mr Patten could do without. It could end by doing precisely what he wishes to avoid - blur all the lines. By forcing American policy-makers into opinionating on Hongkong under the eye of the media, the row will be seen as another human rights blot on China's copy book. Mr Sutter reckons this is perfectly possible. ''The logic of it argues that Patten will get a warm reception in Washington and there is potential for China getting angry. ''Some policy-makers in Congress might be inclined to associate with Patten's ideals.'' What follows from there is surely clear, with US-China relations already tense. It means more fodder for the antagonists, to the Representatives who are all for withdrawing China's MFN status. Already at their disposal, and in addition to the three big evils - human rights, arms proliferation and a burgeoning trade deficit - are a host of issues ready to be called on when the fight turns really nasty. Hongkong is certainly a useful card to have tucked up the sleeve when arguing, from a Western standpoint, that China still needs to be more heedful of basic human rights. In a similar vein, there are Tibet and Taiwan. Supplementary to the trade deficit, there is China's reluctance to implement measures to improve market access. There is Radio Free Asia, which China is totally opposed to as an attack on its sovereignty. None of these is new, but all are capable of being rehashed and whipped up into the MFN debate.