MERIDA, Mexico – President Bush sought to soothe strained ties with Mexico on Tuesday by promising to prod Congress to overhaul tough U.S. immigration policies. But Mexican President Felipe Calderon criticized U.S. plans for a 700-mile border fence and said Bush must do more to curb American drug appetites.

Mexico was the last stop on Bush’s five-nation Latin American tour and the one where the political stakes seemed the highest.

Bush walked a high wire. He wants to improve frayed ties over immigration and drug trafficking and the Iraq war but without alienating supporters back home, particularly Republican lawmakers advocating stiff penalties against undocumented workers.

The president also was distracted by problems at home.

Attorney General Alberto Gonzales acknowledged mistakes were made in the firing of eight federal prosecutors and that the White House was involved in discussions of who would be dismissed and when.

This was Bush’s first meeting with Calderon since the Harvard-educated Mexican conservative took office Dec. 1 after a razor-thin victory.

They clashed, though gently.

Welcoming Bush to a restored hacienda on the sun-drenched Yucatan Peninsula, Calderon said it would be hard to reduce Mexico’s drug production while demand remains high in the United States.

“We need the collaboration and the active participation of our neighbor,” Calderon said.

Bush and Calderon – both pro-business conservatives – acknowledged their differences and vowed to work together.

Calderon said it was time for a fresh start to “direct our relationship toward a path of mutual prosperity.”

“Geography has made our countries neighbors, but the choice we’ve made for each other is a choice for freedom,” said Bush. “And that choice has made us friends.”

Happy talk aside, relations between the two neighbors have worsened since Bush last year signed a law calling for construction of fencing along the long border the two countries share. Calderon has ridiculed the fence – a mix of physical and high-tech barriers – and likens it to the Berlin Wall.

Calderon argued that the fence would do little to stem illegal migration. But he also praised Bush for pushing for immigration reforms and acknowledged that improving economic conditions and generating more jobs in Mexico “is the only way in order to truly solve the migratory issue.”

It is questionable whether the full 700-mile fence will be built. A bill authorizing the fence did not come with any new funding, and the $1.2 billion that Congress previously approved is not enough. A 14-mile stretch under construction in the San Diego area is estimated to cost $126.5 million.

Homeland Security Secretary Michael Chertoff said last month that border officials over all 700 miles may not be necessary.

Bush has been having a hard time lining up support from his own Republican party for his proposals to establish a guest worker program and a path to citizenship for some of the 12 million undocumented workers already in the United States. He has said he hopes for movement, at least in the Senate, by August, but he faces daunting obstacles.

“In the debate on migration, I remind my fellow citizens that family values do not stop at the Rio Grande River, that there are decent, hard-working honorable citizens of Mexico who want to make a living for their families,” Bush said as he stood beside Calderon. “And so, Mr. President, my pledge to you and your government – but, more importantly, the people of Mexico – is I will work as hard as I possibly can to pass comprehensive immigration reform.”

Calderon’s complaints about the fence marked the second day in a row that Bush drew a rebuke from a host. In Guatemala on Monday, President Oscar Berger complained about roundups in the United States of undocumented Guatemalans.

Presidential counselor Dan Bartlett said such reactions are to be expected. In Mexico and in Guatemala, as in the United States, migration “is a very emotional debate,” Bartlett said. He said Bush wasn’t taken off guard by the criticisms. Those leaders “are very concerned about their fellow citizens that are living in the United States at this time,” Bartlett said.

The president and his wife, Laura, also were taking in a tour of the nearby Uxmal Ruins, the remains of an ancient sprawling Mayan city.

Security was extremely tight in Merida. Schools were closed. The area around the hotels where Bush and Calderon are staying was guarded by police and surrounded by metal barriers.