WASHINGTON (AFP) - US President Barack Obama said Tuesday that he was confident he could make a case for the ambitious TPP Pacific free-trade deal as he began pressing for its ratification by Congress.

A day after 12 countries reached agreement on the Trans-Pacific Partnership following gruelling Atlanta negotiations, Mr Obama told agriculture and business leaders that the deal is good for them.

"I've said repeatedly that I would only sign an agreement and present an agreement to Congress if I could be absolutely certain that it was good for American workers and good for American businesses, good for American farmers and good for American ranchers, and good for American manufacturers," he said. "We have met that standard in this agreement."

Although the details of the agreement will not likely be made public for weeks, congressional leaders have already expressed reservations over the TPP deal, which would fashion the world's largest free-trade zone "made for the 21st century".

Mr Obama emphasised that Congress, the public and other stakeholders would all get to see the entire agreement before it goes to a vote in the Congress, expected to take at least three months.

Negotiated in secret, the TPP pact has some 30 chapters on issues from intellectual property protections to handling foreign investor disputes to enforcing labour rights, and a number of annex agreements on specific tariff cuts between specific countries.

"There's going to be a long, healthy process of discussion and consultation and debate before this ever comes to an actual vote," Mr Obama said.

"But I'm also confident that the case to be made for why this is good for America is sufficiently strong; that ultimately we're going to get this done, and it will be an enormous achievement for us to be able to make sure that 40 per cent of the world's economy is operating under rules that don't hurt us."

"Under this agreement, we, rather than countries like China, are writing the rules for the global economy," he added.