Fox and President Bush will instead endorse a set of guidelines for regulating the flow of migrants between the two nations, leaving the details to b worked out by aides, officials say.
And when Mr. Bush sits down with Fox on Wednesday, the discussion of immigration, the main item on the agenda, will have as much to do with domestic policy as foreign affairs.
Mr. Bush and Fox both want to reform the current system to make it legal, safe and humane. But if they are to get anywhere, they will have to deal with those such as Rep. Tom Tancredo, R-Colo., chairman of the congressional immigration reform caucus.
He says there is an "immigration crisis" in this country because of the "massive" numbers who arrive on America's shores illegally. He believes they should be deported, and has introduced legislation to impose a five-year moratorium on immigration, exempting only close family members of U.S. citizens.
Tancredo's views may not be mainstream, but many others share his concerns about current high migration levels - and the prospect that Mr. Bush has expressed a desire to legalize many of those who came here without documents.
Now CBS News reports that, in the face of such opposition, Mr. Bush is backing off his push to grant legal residency to up to 4 million undocumented Mexicans already in the U.S., as well as his proposed guest worker program to allow Mexicans to fill job Americans don't want.
Many in Congress and elsewhere - the business community, labor activists and civil rights groups - agree with Mr. Bush and Fox that the current system is deeply flawed. Administration officials say opinions on Capitol Hill are so diverse that obtaining a majority will be a daunting task.
Fox is expected to have an attentive audience Thursday when he makes his case on migration and other issues before a joint meeting of Congress.
"The current policies are broken," said Frank Sherry, executive director of the National Immigration Forum, a pro-immigration group. He compared the situation to a superhighway with a speed limit of 35 mph: "It doesn't slow traffic and invites illegality."
No one underestimates the mind-boggling intricacies of the issue; indeed the favorite word of administration officials in discussing it is "complex."
Mr. Bush and Fox agreed in February to look at migration reform. Now, more than six months later, little headway has been made on the details, and some believe a concrete proposal won't be ready until after the 2002 mid-term U.S. elections.
Fox has impressed many observers with the way he has been able to set the agenda for U.S.-Mexican relations. He came here with an immigration reform message last year before his inauguration and has not wavered from it.
Immigration will dominate the talks, bu U.S. officials said a host of other cross-border issues will be dealt with - drug trafficking, truck safety, the environment, water and energy. All will receive an airing when cabinet officers from both countries and lower level officials meet at the State Department on Tuesday. They will divide into 16 working groups.
When Fox and Mr. Bush meet the following day, they will have a modest goal on the migration question: an agreement on basic principles that will govern future deliberations. There will be no discussion of the numbers of Mexicans who might benefit from any future reform proposal, officials said.
Fox believes the time has come for Americans to recognize what he sees as obvious: Mexican workers are needed in the United States, they are productive and they should be accorded respect.
He does not call for immediate amnesty for Mexican migrants - U.S. officials believe there may be as many as 5 million here illegally - but says American laws should be amended so they receive health, education and labor rights and can work without fear of deportation.
The administration is considering proposals to allow some to earn legal status through the grant of work permits and eventually "green cards" symbolizing permanent residency under specified conditions.
On Friday, White House spokesman Ari Fleischer tried to put the discussion on immigration in historical context.
"What you will see is a concerted effort by Mexico and the United States together to deal with immigration issues - and that's a big break from the past when Mexico pursued its policies, the United States pursued its and the two seldom talked and never reached any agreements," he said.
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