NEW ORLEANS — For a summit of three countries doing nearly $1 trillion worth of business with each other every year, President Bush’s two-day meeting with his Mexican and Canadian counterparts began here yesterday as a decidedly low-voltage affair.

But despite the quiet start, the annual event is taking place against the backdrop of the U.S. presidential campaign, which has deepened the political sensitivity of their efforts to expand trade and wrestle with other issues, such as immigration and border congestion.

At the end of a meeting with Prime Minister Harper of Canada, Mr. Bush said the talks came at an “opportune time” to reaffirm the trade relationship among the three countries, an unstated reference to the campaign to succeed him.

President Calderon of Mexico was more direct, saying that the North American Free Trade Agreement “has come under criticism.” And, in a photo session with Mr. Bush, he noted that, although America was “going through an electoral process,” the two countries needed to solve immigration issues “with respect and responsibility.”

The meeting is the fourth annual conference between the leaders of America, Canada, and Mexico to deal with mutual economic and security issues. It is the last scheduled summit of the three countries before Mr. Bush leaves office in January.

The summit will focus on trade, immigration, and cross-border drug and weapons smuggling just as free trade agreements and NAFTA in particular are under more political attack than at any time since the America-Canada-Mexico agreement began eliminating tariffs and other barriers to North American trade 14 years ago.

Three-way trade among America, Canada, and Mexico has grown since 1994 to $930 billion from about $290 billion, according to American government statistics. But Public Citizen’s Global Trade Watch, long an opponent of the pact, said the increase was largely the result of a “massive surge in imports” into America, bringing with it what the group calculated was a 691% increase in the trade deficit attributed to NAFTA.

And as fears grow that the American economy has fallen into recession, supporters of the trade deal have faced calls for changes, first during the presidential primary in Ohio and now in Pennsylvania, where steel mills with good jobs have closed from Pittsburgh to Bethlehem.

“We want to find ways to, frankly, convince the American people … that this is an arrangement that’s worked for us, and it’s also worked for our neighbors. It’s been a win-win situation,” the White House National Security Council’s senior director for Western hemisphere affairs, Dan Fisk, said. “There’s nothing broken. Why fix a success?”

The president and chief executive of the U.S. Chamber of Commerce, Tom Donohue, said that Pennsylvania has benefited from NAFTA more than America as a whole, with 40% of its exports going to Canada and Mexico, compared with 35% of all American exports going to those countries. Manufactured goods account for 94% of the state’s exports.

But Global Trade Watch said 220,000 Pennsylvanians have lost their jobs because of NAFTA and the liberalization of trade rules that accompanied the creation a year later of the World Trade Organization.