CANCUN, Mexico (AP) – President Bush said Friday the United States believes it is important to enforce laws protecting borders and told the leaders of Mexico and Canada that was crucial to keeping prosperity alive.

He also reiterated strong support for a “guest worker” program that would allow undocumented immigrants already in the United States to remain in the country to fill low-paying jobs that Americans won’t take.

Bush declined to say whether he would veto legislation that did not contain such a provision.

“I want a comprehensive bill,” Bush said at a joint news conference with Mexican President Vicente Fox and Canadian Prime Minister Stephen Harper.

The three-way meeting in the Mexican resort city of Cancun came as the U.S. Congress is embroilled in an intense debate over immigration legislation.

Bush also defended a new U.S. requirement, to take effect Dec. 31, 2007, requiring all American and Canadian travelers to carry a passport when they cross into each other’s country.

Harper said he had expressed Canada’s concern to Bush over the new restriction.

But, Bush said, “Congress passed the law and I intend to enforce the law.” He said he believes that if properly implemented the program “will facilitate travel and facilitate trade, not hinder travel and trade. I think we can be wise about the use of technologies.”

The three leaders vowed to forge closer ties on trade, energy, combating common problems like the bird flu and in raising standards of living across North America.

“You can’t achieve a standard of living increase for your people unless you have a prosperous neighborhood,” Bush said

Said Fox: “Now we have the alliance both for security and for prosperity _ one as important as the other.”

The news conference was held in an indoor tennis court, decked out with enormous maps of North America and a white backdrop with mammoth video screens flanking the three leaders’ podiums.

At issue on the immigration controversy is a debate over a proposal that would legalize an estimated 11 million illegal immigrants in the United States and expand guest worker programs for an estimated 400,000 immigrants each year.

Both Bush and Fox support temporary guest-worker programs for Mexicans who come to the United States.

A bill now being debate in the Senate contains such a guest-worker proposal. The House has passed rival legislation to tighten border security. Bush has broadly endorsed the Senate approach, saying he wants a comprehensive bill.

Bush also talked about Secretary of State Condoleezza Rice’s trip to Europe to meet with U.S. allies to try to forge a common approach to confronting Iran on its nuclear program.

“There is common agreement that the Iranians should not have a nuclear weapon, the capacity to make a nuclear weapon or the knowledge as to how to make a nuclear weapon,” he said.

Bush said that with such a weapon Iran “would pose a serious threat to world security.”

At the same time, he offered U.S. assistance to victims in Iran of three strong earthquakes that reduced villages to rubble in the western part of the country earlier riday, killing what officials estimated were at least 66 people and injuring about 1,200 others.

The meetings here were aimed at strengthening North American relations and building on the trade increases that have resulted from the 12-year-old North American Free Trade Agreement. Canada and Mexico are the United States’ top two trading partners.

Harper, in his first meeting with Bush since taking office two months ago with a promise beforehand to strengthen U.S. ties and spoke glowingly of the countries’ close relationship. But he also made it clear there is a serious sticking point: He said he was taking Bush “at face value” when the U.S. president said he wanted to resolve a long-standing dispute over U.S. tariffs on Canadian softwood lumber.

“I just reminded the president that Canada’s position on this is very clear, and if we don’t see a resolution, Canada is certainly going to continue to pursue all its legal options, as well as enhanced support for our industry, through this battle,” Harper warned.

The immigration issue has united Bush and Fox, whose friendship dates back to Bush’s time as Texas governor but was strained over Fox’s objections to the war in Iraq. But immigration has divided Bush’s Republican party, with business interests who want cheap labor battling conservatives who want a tough policy against illegal immigrants.

At a news conference Thursday in Washington, a dozen House Republicans blasted the Senate bill. Bush was not immune to their criticism.

“I don’t think he’s concerned about alienating voters, he’s not running for re-election,” said Rep. Tom Tancredo of Colorado. “I wish he’d think about the party and of course I also wish he’d think about the country.”

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On the Net:

U.S. Trade Representative: http://www.ustr.gov

White House: http://www.whitehouse.gov