The world economy is supposed to be globalising at breakneck speed. Yet more and more international trade - generally held to be a driving force forces of globalisation - is not global, but regional.

The World Trade Organisation says 43 per cent of all trade is conducted inside regional trade agreements (RTAs) between two or more countries. It says the figure may rise to 51 per cent by 2005, when the number of RTAs in force and notified to it may have grown to more than 180 from 113 last year.

Few issues divide trade policy makers more sharply than this apparently perverse trend. For some, RTAs are positive, freeing trade between participating countries and progressively constructing the basis for multilateral liberalisation.

US President George W. Bush's administration, which is pressing for a Free Trade Area of the Americas (FTAA), embracing all countries in the hemisphere except Cuba, and is pursuing several bilateral deals, has strongly defended that view. It has pledged to seek liberalisation "multilaterally, regionally or bilaterally."

It is also argued that negotiations between neighbouring countries achieve results faster than cumbersome world trade rounds, and that RTAs help cement domestic economic reforms and market-based economic policies.

Other observers, including many trade economists, are much more sceptical. While conceding that RTAs can expand trade between member countries, they point out that unless barriers to third-country imports are also removed, such gains are at the expense of outsiders.

Another objection is that RTAs create a tangle of different, but partially overlapping, regulations, such as rules of origin designating which goods qualify for preferential treatment.

Some critics also complain that negotiations on RTAs, which can last several years, retard rather than promote liberalisation, because countries delay unilateral liberalisation in order to store up "bargaining chips" they can trade off against concessions by prospective partners.

Finally, RTAs are often criticised as distracting political attention from the rules-based multilateral system. Such concerns are particularly acute when - as in the past few years - countries' commitment to multilateralism has appeared to falter.

It is hard to be sure which view is correct, because no clear criteria for judging the economic effects of RTAs exist. WTO rules are vague and have hardly ever been applied, not least because almost all its members belong to at least one RTA.

One point on which the evidence is fairly conclusive is that RTAs are rarely initiated purely for commercial and economic reasons at all. More often, politics is a more important inspiration.

The World Bank observed in a recent report: "The purpose of regional integration is often political, and the economic consequences, good or bad, are side effects of the political pay-off."

Indeed, there appear to be as many specific motivations as there are RTAs. Mr Bush's enthusiasm for FTAA owes much to his desire to underpin security and political stability in Latin America. Singapore's recent pursuit of RTAs is rooted in its growing sense of regional insecurity since the 1997 Asian financial crisis.

For the European Union, the oldest and still the most active enthusiast of RTAs, they are an attempt to compensate for its lack of a common foreign policy, while for Australia and New Zealand, two more recent converts, they are intended to avoid exclusion from trade blocs emerging elsewhere.

Along with their growing popularity, RTAs' most striking feature is that they are no longer confined to neighbouring countries. Japan, for instance, is studying or negotiating deals with partners as far-flung as Canada, Mexico and Australia - as well as with Korea and Singapore, while New Zealand and Chile are also in talks.

However, it is uncertain the rush to conclude RTAs, which has gathered pace since the late 1990s, will produce hoped-for results. Experience suggests the most successful arrangements work because they involve economies that are geographically close and at similar stages of development.

The EU's customs union meets those standards. But the same cannot be said of the ambitious recent proposal to create an RTA embracing the Association of South East Asian Nations (Asean) and China. Meanwhile, the severe strains on Mercosur, the four-nation Latin American grouping, underline the difficulty of harnessing together economically unstable markets.

Indeed, many of the more recent RTA proposals appear to fall into one of two categories. Those that are successfully consummated are often between economies, such as Singapore and New Zealand, that are already open. As a result, they achieve little additional liberalisation.

In contrast, prospects for the proposed RTA between Japan and South Korea look doubtful, because of both countries' highly protected agricultural markets. In such cases, agreements are unlikely to amount to much more than loose commercial cooperation deals which involve little or no removal of border barriers.

The realisation that the likely economic gains from many RTAs under discussion are limited may, in time, cool recent enthusiasm for them. Interest may also be dampened, once negotiations on a new trade round get under way.

One reason is that a trade round involving more than 140 governments offers far bigger scope for mutually advantageous trade-offs than does bargaining with a more restricted group of countries. Many US business lobbies, for instance, see much more to be gained from a round than from the creation of a FTAA, whose prospective Latin American members account for only 6 per cent of world imports.

Another reason is simply a shortage of negotiating capacity. Even the US may find its resources stretched if it seeks, as it currently plans, to engage simultaneously in talks on a FTAA and on a global trade round.

Stricter WTO disciplines on RTAs could also limit their spread. Ministers agreed in Doha this month to review the organisation's rules and machinery for judging RTAs, as part of a new trade round. But given countries' past reluctance to submit themselves to effective curbs, most observers doubt the talks will yield any radical breakthroughs.