Two years after the acrimonious collapse of its Seattle meeting, the World Trade Organisation is back in business. This month's agreement by its 142 members in Doha, capital of the Gulf state of Qatar, to launch a trade liberalisation round has given a boost to global economic confidence and much-needed new impetus to the WTO.

In one sense, the Doha meeting succeeded because it was too important to fail. As Mike Moore, WTO director-general, and many trade ministers emphasised beforehand, another serious setback would have sent a dire political signal about governments' ability to face up to the most serious global economic problems for at least a decade.

A debacle would also have weakened the WTO's authority and imperilled the rules-based multilateral system. Many observers believe it could have precipitated the fragmentation of the world economy into hostile regional trade blocs and led to outbreaks of protectionism.

In truth, fear was probably the biggest driving force behind the deal. But several positive factors also contributed. They included better preparation than before Seattle, close co-operation between the US and the European Union and greater involvement of developing countries, many of which had previously been indifferent or hostile towards a round.

However, as many participants have observed, Doha was merely the start - not the end - of negotiations. Whether the spirit of compromise which made agreement there possible will endure, and what the eventual result will be, will only become clear after the round begins in January.

The first test will be to agree exactly what was decided in Doha. The need hastily to paper over divergent positions, not to mention sheer exhaustion, produced an agenda so riddled with ambiguity that it seems likely to keep trade negotiators haggling for months. That WTO members with conflicting interests have proclaimed the agenda a victory shows how open it is to multiple interpretations.

Even the proposed three-year timetable for the round looks doubtful. Serious bargaining on agriculture and some other tough issues are not due to get into their stride for two years, while the climax of the talks is scheduled, implausibly, to coincide with the next US presidential election campaign.

Another, as yet incalcula ble, element will be the impact of China's WTO membership, which was formally endorsed at Doha. Accession by the world's most populous economy is widely expected to shift the political balance within the organisation - though nobody is yet sure in exactly what direction.

Equally uncertain at the time of writing was the fate of US President George W. Bush's efforts to secure "fast track" trade negotiating authority, on which the House of Representatives has tentatively scheduled a vote early next month.

Although the US does not technically need "fast track" to start trade talks, the vote will be an important psychological test of US commitment to the WTO, and rejection would shake the confidence of its trading partners.

What is clear, nonetheless, is that, even after eight previous trade rounds, there is plenty more work on lowering trade barriers to be done. One indication is a recent World Bank estimate that their elimination could add as much as $2,800bn to global economic income by 2015.

However, harnessing the gains will involve a struggle. For every opportunity for liberalisation, there is an interest group determined to resist it - and even the positions of countries supposedly preaching open markets are not always clear cut.

Liberalisation efforts in the new round will focus on three main areas:

* Agriculture: This is the most protected sector and the one where liberalisation would most benefit exports by developing countries, which dominate WTO membership.

Despite cuts mandated by the Uruguay Round, tariffs are on average three times higher than on industrial goods and, in some cases, exceed 500 per cent. The EU, Japan and Korea are likely to resist further reductions, and even some ostensible free traders, such as the US and Canada, protect certain imports.

It is also unclear how firmly the US will continue to support the campaign by the 18-member Cairns Group of farm exporters for cuts in EU export subsidies. Washington is torn between seeking more open world markets and responding to US farmers' demands for ever larger domestic subsidies.

There is also a risk that removal of existing barriers could be followed by erection of new ones - notably import curbs imposed in the name of health and safety. The EU is widely suspected of wanting greater freedom to apply such measures, after being racked by food scares that have undermined public trust in its own regulatory systems.

* Industrial tariffs: Although these have been reduced, on average, to about 4 per cent in rich countries and 15 per cent in poor ones, rates for many individual items are much higher.

The US and EU charge duties of more than 20 per cent on truck imports, while duties on sports footwear are more than 48 per cent in the US and 27 per cent in Japan.

Arguably an even bigger barrier are anti-dumping measures, which have proliferated and spread to developing countries since the 1997 Asian financial crisis. Although WTO negotiations are due to be held on curbing anti-dumping, strong lobbies in the US and EU will resist rapid change.

* Services: As the fastest-growing activity in most economies, these appear to offer the greatest scope for liberalisation. However, after September 11 the US and some other countries may be reluctant to lower barriers in areas such as air transport and freer movement of skilled workers.

There are two other potential obstacles. One is that the WTO has not so far been effective in getting members to liberalise services faster than they were already doing. Its two agreements to date, in financial services and telecoms, entrenched existing policies rather than opening markets further.

Second, services liberalisation depends on establishing effective national regulatory regimes and enforcement. That is a complex task, in which the WTO has no real experience.

On the other hand, pressure from trading partners in a round can strengthen the hand of governments in facing down domestic opposition to reform.

Despite protests by anti-globalisation campaigners, there is little sign that enthusiasm for market-based reforms has diminished around the world - and recent studies suggest that open economies have prospered more than closed ones.

How these different forces will play out in practice may not become clear for several years. But once negotiations on a round begin in earnest, launching it may start to look like the easy part.