Special rules apply to trade in agricultural products, motor goods, energy and textiles.

Fourteen long months of negotiations by 18 working parties across six broad topics culminated in October last year when the trade ministers of Canada, Mexico and the United States initialled the legal text of the agreement. In December, the three heads of government signed the treaty.

The Canadian parliament has already ratified the agreement, and Mexico's parliamentary approval is guaranteed.

Full implementation - due to take effect on January 1, 1994 - hinges on the United States' Congress.

While it was the former Republican president George Bush who signed the deal, Democratic President Bill Clinton is now strongly in favour of ratification, having added key side deals, covering labour and environmental protection, to the main treaty.

The Senate is expected to approve the deal, but the House of Representatives is deeply divided - one third is in favour, one third against and one third undecided, according to Agustin Gutierrez Canet, Consul General of Mexico in Hong Kong.

''The outcome depends on just how the Clinton team sets about persuading the middle third,'' he said.

Mr Clinton has this week launched a formal campaign to win ratification, and has the pledged support of 280 leading US economists, including 12 American Nobel Laureates.

The campaign also includes pro-NAFTA television commercials, funded by private-sector backers.

However, a great deal of opposition remains.

''Ross Perot is strongly against [the deal], and he actually bought media time and space to show anti-NAFTA advertisements,'' said Mr Gutierrez Canet.

''Also opposed is the major American trade union body, the AFL-CIO, and numerous environmental groups.'' Jaime Aletorre, president of the Mexican investment board, highlighted two newspaper headlines, both from February 3, which dealt with a study into NAFTA's likely impact.

One, from The New York Times, said: ''Study says trade pact will aid US economy''.

The other, from The Wall Street Journal, read: ''Mexico is viewed as the clear winner from free trade pact in study''.

Mr Aletorre said there would be three major winners from the agreement - the US, Mexico and Canada.

''I'll share a third newspaper headline on the same story, this one from the Investor's Business Daily. 'Study sees widespread NAFTA benefits'. Perhaps that says it best.'' Gabriel Alvardo, Mexico's Trade Commissioner in Hong Kong, has no doubts that Mexico is sure to reap substantial gains from NAFTA.

''The broad framework of structural reform in Mexico has dramatically opened up our economy,'' he said.

''The very fact that we ran a US$20 billion trade deficit last year is proof of that.

''But look at the make up of that sum and you'll see that a high proportion comes from the import of capital goods, such as machine tools.

''This means that we are getting all the right ingredients into place for the solid industrial and economic growth to come.

''In promoting Mexico as an investment opportunity, we see the NAFTA deal as an extra attraction, a bonus, but we would insist that the fundamentals are in place.

anyway.''