President Bush and Mexican President Vicente Fox will meet Wednesday at the White House to discuss the issue of Mexican migrants living in the U.S., and even though the leaders agree on many of the points, Bush has said there probably won't be a detailed agreement.

Before Bush can reach an agreement with Mexico, he needs to reach one with Congress.

"Immigration is one that is a complex issue," Bush said. "President Fox knows that the issue will require more than just the administration's involvement; it requires a willing Congress to address the issue."

An estimated three million Mexicans — and as many as five million — are living illegally in the U.S.

Even before Fox was inaugurated as Mexico's president, he came to the States to push an immigration reform agenda. In February, the leaders met and agreed to look at reforming immigration laws.

Reforms proposed by the Bush administration include granting some migrants work permits that would eventually allow them to gain permanent residency status.

Fox wants the U.S. and states to change laws so migrant workers receive health, labor and education benefits. He also supports guest-worker programs as a favorable alternative to immediate residency.

Standing between the two leaders and a deal are a spectrum of opinions in Congress. On the far opposite side of the issue, chairman of the congressional immigration reform caucus Rep. Tom Tancredo, R-Colo., believes that the solution to the "immigration crisis" is to deport the workers and impose a five-year moratorium on all immigration.

Fox will have a chance to take his case to Congress on Thursday, when he will address a joint session.

Some people think a deal in Congress is impossible until after the 2002 U.S. elections, where many incumbents and candidates will have to clarify their position.

Most observers agree, however, that the current system needs to be changed. "The current policies are broken," said Frank Sherry, executive director of the National Immigration Forum, who said the current policy "invites illegality." 

The official visit will begin on Tuesday at the State Department, when Mexican and U.S. cabinet officers will form 16 working groups to tackle problems like drugs, power, and the environment. On Wednesday, Bush and Fox will meet and try to agree to broad principles for immigration reform that will guide future talks.

"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," White House spokesman Ari Fleischer said Friday.

For Fox, who has been praised for his ability to control the agenda in talks with the U.S., the goal will be to get Congress to see things the way Bush already does — that Mexican workers are productive members of U.S. society and deserve recognition.

The Associated Press contributed to this report.