"I'm amused by the difference between what actually takes place in the meetings and by what some are trying to say takes place," said Mr. Bush, responding to concerns raised by conservative and liberal groups and some U.S. lawmakers.

"It's quite comical actually, to realize the difference between reality and what some people on TV are talking about."

Canadian Prime Minister Stephen Harper joked that a superhighway rumored to be in the works linking the three countries could also be "interplanetary."

The two leaders and Mexican President Felipe Calderon spoke at a press conference here in a countryside resort, halfway between Ottawa and Montreal, to cap two days of meetings.

Mr. Bush said it is important for the U.S. to work with Canada and Mexico on facilitating trade while securing their borders, under the Security and Prosperity Partnership of North America (SPP), a series of negotiations started in 2005.

Mr. Bush said the charges of a plot to form a North American Union were "political scare tactics."

"You lay out a conspiracy and then force some people to try to prove it doesn't exist. That's just the way some people operate," Mr. Bush said.

Mr. Harper said the trade talks were far more mundane than many realize, citing a morning meeting with business leaders at which one CEO complained that "the rules for jelly bean contents are different in Canada and the United States."

"They have to maintain two separate inventories. Is the sovereignty of Canada going to fall apart if we standardize the jelly bean? You know, I don't think so," Mr. Harper said.

Mr. Calderon said there were "myths" about the SPP, and joked, "I'll be happy with one foot in Mexicali and one in Tijuana."

The rumors of an EU-style plot, which started out on obscure Web sites and talk radio, have since been picked up by CNN anchor Lou Dobbs and have now gained traction among some of the House Republicans who successfully derailed Mr. Bush's immigration-reform plan.

A group of 21 Republican congressmen and one Democrat — Rep. Nancy Boyda of Kansas — sent Mr. Bush a letter earlier this month expressing "serious and growing concerns" about the SPP.

White House officials say the SPP is meant to build on the North American Free Trade Agreement, which they say has generated $884 billion in trade among the United States, Mexico and Canada over the past 12 years, while boosting the security of cross-border trade.

But the idea of a plot has gained currency, and the recent fight over immigration policy has only made things worse by aggravating fears about cross-border cooperation with Mexico.

Mr. Bush also spoke at the summit about Iraq, saying that if the Iraqi government, led by Prime Minister Nouri al-Maliki, does not make progress on passing key laws, then the people of Iraq will elect different leaders.

"They will make decisions, just like democracies do," Mr. Bush said.

Mr. Bush and Mr. Harper also said they discussed Canada's displeasure with U.S. requirements that Canadians must show a passport when coming to the U.S., and disagreement over Canada's claim of sovereignty over the Northwest Passage.

No compromises were reached, but both leaders said their strong relationship remained intact nonetheless, and Mr. Bush thanked Canada for its commitment of 2,500 troops to Afghanistan.

Mr. Bush and Mr. Calderon discussed an aid package from the U.S. to help Mexico fight drug trafficking, but said they have not yet reached an agreement.

Mr. Bush also said the U.S. is ready to help Mexico if it needs money or aid dealing with the effects of Hurricane Dean, which hit the Yucatan Peninsula yesterday.