President Bush is in Mexico ahead of Thursday meetings with the leaders of Mexico and Canada.

This will be the first tri-lateral summit involving Canada's new prime minister, Stephen Harper. President Bush and Mexican President Vicente Fox will both meet separately with the Canadian leader ahead of a joint news conference Friday.

White House Spokesman Scott McClellan says the talks will focus on a Security and Prosperity Partnership between the countries that began last year in Texas to strengthen North American security and economic development. "This is a way to build upon our efforts to really make sure that North America is more integrated and remains competitive in this global, changing economy that we live in," he said.

McClellan says President Bush looks forward to concrete ways to move that partnership forward.

Duties on softwood lumber imports are expected to dominate the president's talks with the Canadian leader. Immigration will be at the forefront of his meeting with President Fox.

The Senate Judiciary Committee this week approved a bipartisan bill that would establish a temporary worker program offering permanent residency and U.S. citizenship for many of the estimated 11 million illegal immigrants in the country. President Bush backs that provision, but it is facing opposition from many within his own political party who believe it is a form of amnesty for people who entered the country illegally.

McClellan says it is not an amnesty. He says President Bush will reiterate his commitment to comprehensive immigration reform and the responsibilities that both countries have in securing their common border.

McClellan says the legislation will help establish an objective, rational, and orderly immigration system to relieve pressure on border patrols. "It will allow our law enforcement officials and border patrol agents to focus on those who are coming here for the wrong reasons - the criminals and the drug dealers and the terrorists," he said.

In recent weeks, protesters across the country, most of them Hispanic, have held demonstrations against restrictions on immigration. Meanwhile, America's largest labor union opposes the guest worker program called for in the proposed legislation, saying it will lower wages and worsen working conditions.

The legislation must pass the full Senate and be reconciled with a much stricter bill that passed the House of Representatives in December. That measure would make it a felony to be in the country illegally and would penalize employers who hire illegal aliens.