Washington: US President Barack Obama and Singapore's prime minister on Tuesday made impassioned sales pitches for the benefits of a pending Trans-Pacific trade deal during a state visit by the head of the Southeast Asian commercial hub.

Both the US and Singapore are signatories to the 12-nation Trans-Pacific Partnership (TPP), which Obama hopes Congress will approve before he leaves office in January.

Obama and Prime Minister Lee Hsien Loong stressed that while concerns about the fate of workers in the increasingly global economy are well founded, the US cannot turn its back on trade.

"We are part of a global economy. We are not reversing that. It can't be reversed because it is driven by technology ... and the fact that the demand for products inside of our country means we've got to get some things from other places," Obama said at a joint Press conference with Lee.

"The notion that we're going to pull that up root and branch is unrealistic," he said.

The TPP faces a battle in Congress. Some US voters blame trade deals for shutting factories, shipping jobs overseas and favouring corporations over the environment.

The pact is also opposed by presidential candidates Hillary Clinton, a Democrat, and Donald Trump, a Republican.

Obama said he looked forward to making the case for the trade deal to MPs from both parties after the November 8 presidential election, when Congress will be in a lame duck session ahead of the inauguration of Obama's successor.

"I think I've got the better argument," he said. "Hopefully after the election is over and the dust settles, there will be more attention to the actual facts behind the deal. It won't just be a political symbol."

Obama believes the TPP will fix problems in a previous trade deal, the 1994 North American Free Trade Agreement, and will create jobs by allowing people around the world to buy US products. The TPP aims to liberalise commerce in 40 per cent of the world's economy and would be a check against China's influence in Asia.

Lee cast the deal as pivotal to the United States' relationship with Asia. If the US were to pull out now, it would be like a bride not arriving at the altar, he said.

"In terms of the economic benefits, the TPP is a big deal," Lee said. "In terms of America's engagement of the region, you have put your reputation on the line."

Dropping out of the trade deal could harm US relations with its allies in Asia, and may cause Japan to question whether it can continue to depend on the US for security, Lee said.