NEW ORLEANS — President Bush pulled the leaders of Mexico and Canada into an unusually direct involvement in his domestic political efforts to expand free trade on Tuesday when his two North American allies joined him in a foray into both congressional politics and the presidential campaign.

President Felipe Calderon of Mexico and Prime Minister Stephen Harper of Canada lent their weight to what has been something of a lonely campaign by the president as he has traveled the country to make pro-trade speeches and angry statements about the "petty politics" that he sees threatening one of his administration's major legacies.

They joined Bush in sharply criticizing a decision by the House speaker, Nancy Pelosi, to scuttle a vote on a free trade agreement with Colombia. And indirectly but unmistakably, they rebuffed calls by the two Democratic presidential candidates to renegotiate the North American Free Trade Agreement.

"We talked a lot about the NAFTA, and of course we agreed that this is not the time to even think about amending it or canceling it," Calderon said, appearing with his two counterparts after two days of meetings here in New Orleans in which they trumpeted what they described as the irrefutable economic progress in each of their countries since the agreement was reached in 1994.

"This is the time to strengthen and reinvigorate this free trade agreement among our three countries," the Mexican president added.

Bush has always made his views on trade abundantly clear, but his increasingly critical comments underscored a mounting frustration that the trade issue has stalled in Congress and come under attack by the two Democratic candidates, Sens. Hillary Rodham Clinton and Barack Obama.

Without mentioning either by name, Bush dismissed criticism of NAFTA as "a throwaway political line," suggesting, as one of Obama's own advisers reportedly told Canadian officials, that opposition to free trade involved electoral politics more than policy questions.

Clinton and Obama, facing off in Pennsylvania, where the effects of trade had become a pointed campaign issue in the weeks leading to the primary on Tuesday, repeated their pledges that they would seek to renegotiate the terms of NAFTA. Both Calderon and Harper made it clear that they would not support reopening the agreement.

Both leaders also echoed Bush's warnings that rejecting a free trade agreement with Colombia would undercut not only economies in the region, but also its security.