Washington, Tuesday.

PRESIDENT Clinton launched his campaign for the North American Free

Trade Association treaty today with the help of three former presidents

and a clutch of other officials. It will be an uphill battle.

The United States and Canada have shared a free trade area for several

years. President George Bush and the Mexican leader, President Salinas,

extended it to Mexico. The treaty was signed last year, but it will be

exceedingly difficult to have it ratified by Congress.

Many, perhaps a majority, of Democrats in the House of Representatives

oppose the Nafta treaty because their constituents fear that it will

cost them their jobs. For years there has been a steady attrition of

highly-paid industrial jobs in the United States as firms move

manufacturing plant to cheap-labour countries in Asia and Latin America.

They fear that Nafta will accelerate this.

The Mexicans have already opened their market to American imports.

President Salinas has privatised the banking system, sold off many

state-owned firms, and permitted American-owned factories to open in

Mexico. The result has been a dramatic expansion of the Mexican economy.

Supporters of Nafta claim that Mexican prosperity means more American

jobs, as Mexico increases its imports from the US. The figures confirm

the argument, but there is no denying that many American jobs have moved

south of the border, and more will follow if Nafta is passed.

Ross Perot, who ran as an independent in the 1992 presidential

election and won 20% of the vote, has been leading the campaign against

Nafta. He won many cheers last year by saying ''If Nafta is passed,

there will be a loud sucking sound as American jobs are sucked south.''

As the final version of the treaty was signed today at the White

House, the president spelled out the advantages of Nafta and let former

presidents George Bush, Jimmy Carter, and Gerald Ford say their pieces

in its favour. Mr Carter won the loudest cheers by denouncing Mr Perot.

''Unfortunately, we have in this country a demagogue,'' he said, ''who

has unlimited financial resources and is extremely careless with the

truth.'' He said Mr Perot's campaign might influence Congress unless it

was met by people of courage.

It was a good speech, and a surprising occasion. Former presidents do

not often visit the White House, let alone make public speeches there.

This was the first time Mr Carter has had such an audience since he left

office. He and his wife, Rosalyn, and George Bush had attended the

Middle East signings yesterday and stayed on at the White House.

Mr Carter's speech was preceded by former president Bush and followed

by former president Ford, who spoke equally warmly of Nafta. Only the

deepest sceptics would note that all three were one-term presidents

defeated in bids for re-election.

Opponents of Nafta have denounced it for the past year, and it is

rather late for its supporters to spring into action.

Richard Gephardt, the third-ranking Democrat in the House, is a

sceptic and probably a majority of Democrats in that house oppose the

treaty. Lloyd Bentsen, secretary of the treasury, is reported to be

deeply unhappy at the lack of effort the president has put into pushing

Nafta.

It will need Republican support to pass, and Republican leaders were

in the White House to hear their former leaders and show support. It

will however be difficult for some to resist the chance to humiliate

President Clinton.