By Tom Miles

GENEVA (Reuters) - The head of the World Trade Organization said on Wednesday he would not get into an argument with U.S. presidential candidate Donald Trump, who has described the global trade body as a "disaster" and threatened to quit it.

But WTO Director General Roberto Azevedo told a news conference he thought the arguments in favor of global trade needed to be put more forcefully.

He said he had warned before Britain's referendum last month of the risks of leaving the European Union, saying it would require years of complex trade talks to complete, but "sometimes people don’t want to hear the arguments".

Appearing on NBC's "Meet the Press" on July 24, Trump said U.S. companies that move production to Mexico should be taxed and shrugged off suggestions this would break WTO rules. "We're going to renegotiate or we're going to pull out," he said.

"We think trade is so obviously positive for every economy that it’s like trying to argue with a friend that he needs to breathe," Azevedo said, adding: "I don’t think we do enough in making the case for trade."

Azevedo, who said earlier on Wednesday that he would seek a second four-year term as the head of the WTO, said he was impressed by the number of people who had responded to Trump by speaking up for trade, "sometimes from unexpected quarters".

He declined to comment on what would happen if the United States did withdraw from the 21-year-old trading club, which now boasts 163 members and governs the vast majority of global commerce through a system of mutually agreed rules.

Under President Barack Obama, the WTO has been an important arena for the United States to defend its commercial interests against China, India and other major trading powers.

A debate over trade also raged before Britain's June 23 referendum on leaving the European Union. Britain voted in favor of Brexit despite warnings from Azevedo and others about the risks, and the country now faces years of protracted and complex trade talks to try to extricate itself from the EU.

Asked how to improve the quality of debate and help voters understand the issues, Azevedo said people sometimes make decisions "on a basis of things that is completely foreign to the rationale of the issue that you are discussing. It has nothing to do with how trade helps or does not help".

(Reporting by Tom Miles; Editing by Tom Heneghan)