WASHINGTON -- Over the course of the long presidential campaign, neither candidate has offered much detail on how he’d boost trade, a main engine of economic growth and an increasingly important source of earnings for U.S. farmers and ranchers.

Neither candidate has voiced any support for the stalled global-trade negotiations, called the Doha Round, which was supposed to knock down barriers to trade, especially in farm products. That’s striking given that U.S. exports of goods and services exceeded $2.1 trillion last year.

“One of the problems is that (talking up) trade doesn’t bring you votes,” said Pablo Goldberg, the global head of emerging market research for HSBC Global Research.

Most of the focus on the campaign trail has been on who’ll be a tougher trade-rules enforcer. What little talk there’s been of trade promotion has been vague.

For example, GOP candidate Mitt Romney, mindful of swing-state Florida’s trade with Latin America, lamented in Monday’s foreign-policy debate the “opportunities for us in Latin America we have just not taken advantage of fully.”

However, the United States already has trade agreements in place with Mexico, Central America, Chile, Peru, Panama and Colombia. It buys oil from Venezuela, and Ecuador uses the dollar as its currency. Argentina remains a pariah after defaulting on its debts. That leaves just giant Brazil as the only significant market in Latin America that the U.S. has no pact with.

“Brazil is a pretty protected economy,” said Gary C. Hufbauer, a veteran trade analyst at the Peterson Institute for International Economics, adding that the South American giant has protection levels three times that of China. “And they have a long history, I mean 50 years, of protecting industry.”

President Bill Clinton launched talks to create a hemisphere-wide trade agreement but the negotiations died during the George W. Bush years because Brazil didn’t see a pact as beneficial.

President Barack Obama has supported freer trade during his term, but you wouldn’t know that from his campaign now. Trying to keep a lead in the polls in blue-collar Ohio, which has bled manufacturing jobs, Obama doesn’t tout that trade pacts with South Korea, Colombia and Peru were implemented under his watch.

Global merchandise trade has grown by about 3.7 percent annually since 2005, above the 2.3 percent growth rate for the global economy from 2005 to 2011. The United States and Europe together account for 50 percent of the world’s exports.

Yet both presidential campaigns have chosen to focus on how they’d get tough on trading partners, especially China.

Romney says he’ll label China a currency manipulator on his first day in office, a designation that would allow, but doesn’t require, the United States to impose trade penalties on Chinese products deemed to have hurt specific U.S. companies or sectors.

The president, who similarly railed against China as a candidate in 2008, points to his record in trade enforcement and what he calls a record number of probes and complaints against Chinese products.

“I think that both President Obama and Mitt Romney have compelling positions on China,” said Scott Paul, who heads the Alliance for American Manufacturing, a trade group that represents smaller U.S. manufacturers that haven’t expanded abroad. “I think together they’ve elevated this issue to a point that we haven’t seen for a long time. I welcome that. It’s a discussion that’s overdue.”