DUBLIN (REUTERS) - Companies would race to profit from a free trade agreement (FTA) between the European Union and the United States, bringing a near instant boost to both economies, the head of the US Chamber of Commerce said.

"If they made a deal tomorrow, US and European companies are sitting on a boatload of cash and they'd be moving this thing up as fast as they can move," Thomas Donohue, president of the US Chamber of Commerce, said after a EU-US trade conference in Dublin.

The 27-member bloc and the United States are likely to launch negotiations on a trade deal by the end of June, with discussions set to last at least two years, meaning an accord could enter into force by 2016.

The deal could add 0.5 and 0.4 per cent respectively to European and US gross domestic product, according to a European Commission (EC) report, although it could take a decade to deliver those effects.

Donohue said a deal could deliver benefits more quickly than suggested by the EC report.

"You open a door and say there's money on the other side, there's opportunity to expand, to export, to sell their products, to make partnerships ... You think they're going to wait around til 2027? They'll be through the door before you know it," he said in an interview.

Donohue said it was important politicians and trade officials move quickly and conclude a comprehensive deal as soon as possible.

"There are a lot of people sitting around saying, well we have to take our time. We don't need to take our time. We got millions of people looking for a job," he said.

Donohue said he was optimistic on the prospects of agreeing a free trade alliance, which would remove tariffs and reduce other barriers to trade, if only because both partners were desperate for growth to cut unacceptably high unemployment.

"I believe they will do that for the following reasons: they must, they need to," he said.

The White House notified Congress last month of its plans to begin free trade talks with Europe, in an effort to capitalise on the world's largest trade and investment relationship to spur growth.