After the World Trade Organisation's Cancun meeting collapsed this month, Robert Zoellick, US trade representative, said he would no longer sit by while "won't do" countries blocked progress in the Doha trade round. Instead, he would forge bilateral and regional trade deals with the "can dos".

Mr Zoellick hopes to open US export markets and to spur "competitive liberalisation", unleashing pressures for freer trade worldwide. However, his optimism looks misplaced. "Competitive liberalisation" is an unproven theory, based on questionable empirical evidence. In practice, the approach seems unlikely to do much to expand US exports, while adding to the fast-growing patchwork of discriminatory deals that distort global trade.

Mr Zoellick's big regional project is the Free Trade Area of the Americas. But support in the US Congress is patchy, at best. The talks also face daunting obstacles, not least because the US refuses to discuss cutting its farm subsidies outside the WTO and is reluctant to lower its trade barriers. The outlook has grown even tougher since Brazil, long antagonistic towards the US in the FTAA talks, rallied other developing countries behind a hard line on farm trade in Cancun.

If the US really wants to expand bilateral trade, logic calls for deals with bigger economies. But strained US trade relations with Brazil, China and India make such ties with the leading emerging markets improbable. Japan looks a lost cause, while the European Union's protectionist farm policy is only the biggest of many roadblocks to any plausible transatlantic initiative.

That has left Mr Zoellick trawling for tiddlers. His targets at present are mainly a motley collection of poor and backward countries in Africa, the Middle East and central America, with a negligible share of world output and trade. Even Australia, much the richest prospective US partner, accounts for only 1 per cent of world imports - and its market is already fairly open.

The US has further narrowed its options by subjugating trade to politics. Mr Zoellick and congressional leaders say bilateral partners will be judged by their loyalty to US interests. If they step out of line, they can expect no mercy, as Egypt has found. After hailing the country as a prime candidate for a deal, Mr Zoellick struck it from the list because Egypt failed to support a US challenge to the EU's genetically modified food regime.

The US has an overwhelming advantage in bilateral negotiations; what commercial gains others can expect from them is much less clear. Mr Zoellick said in Cancun that the US had made its best liberalisation offers, which were likely to be scaled back as next year's US elections neared.

Both he and countries tempted by deals with the US need to think again. What is now on offer looks like something only the desperate cannot afford to refuse. The WTO, for all its flaws, is still the best hope for genuine trade liberalisation.