GUADALAJARA, Mexico -- President Barack Obama pressed for a new tone in the United States' relationship with Mexico but found no immediate progress Sunday on the divisions between him and Mexican President Felipe Calderon over the pace of U.S. drug-fighting aid and a ban on Mexican trucks north of the border.

Obama kicked off his second trip to Mexico as president with a friendly 45-minute meeting with Calderon that touched on the vast trade relationship between their two countries, their cooperation on swine flu and the violent Mexican gangs dominating the drug trade on both sides of the border. Their talks came before the start of a lightning-quick three-way summit between the United States, Mexico and Canada.

Often called the "Three Amigos" summit, the meeting of Obama, Calderon and Canadian Prime Minister Stephen Harper began over dinner at a cultural institution in this town near the mountains. The summit's formal talks, the fifth for the three countries, were taking place Monday, followed by a joint appearance before reporters at midday.

During the separate sit-down between Obama and Calderon, the Mexican leader raised his concerns about the speed of implementation of the United States' three-year, $1.4 billion drug-fighting package known as the Merida Initiative. One $100 million installment is being delayed over rising concerns among some in Congress about the Mexican army's abuses.

The U.S. law requires Congress to withhold some funding unless the State Department reports Mexico is not violating human rights during its anti-cartel crackdown, which started in 2006.

Obama told Calderon that human rights is a major priority for him, but also assured him that the State Department is working to prepare a report that recognizes all Mexico's efforts to prevent abuses, said a senior administration official, who briefed reporters on condition of anonymity in order to more freely describe private meetings.

Drug violence has killed more than 11,000 people since Mexico launched its crackdown.

Mexican cities are essentially under siege, and the killings are spilling over the border into the United States and as far as Canada.

Calderon also quizzed Obama on his earlier promise to restore a canceled pilot program that had allowed Mexican truckers to travel into the United States, the official said.

The North American Free Trade Agreement required the United States to grant Mexican trucks full access to its highways by January 2000, but domestic opposition stalled that plan until a 2007 pilot program allowed some trucks. Facing opposition from U.S. labor unions and consumer groups, Obama signed a spending bill that included a ban on spending for the program.

Mexico retaliated by imposing tariffs on dozens of U.S. products ranging from fruit and wine to washing machines.

Obama told Calderon he would work "to try to move forward" but also said Congress has "legitimate safety concerns" about Mexican trucks, the official said.

Outside the sprawling colonial-era building where they met in Mexico's second-largest city, caravans of heavily armed federal agents patrolled the streets. Dozens of police carrying riot gear manned roadblocks meant to keep protesters away.

U.S.-Mexico relations went on a roller-coaster ride during the tenure of former President George W. Bush, driven by a divide over the Iraq war, the United States' building of a border fence and Bush's failure to secure immigration reform. While Obama has, like Bush, emphasized beefed-up border security, he has pledged to renew efforts to push through an immigration overhaul, including a citizenship path for illegal immigrants.

And during his April visit, Obama made a welcome acknowledgment to Mexicans that Americans share the blame for violence south of the border because of drug consumption and gun trafficking.
A major topic of discussion for the three leaders on Monday will be the now-global swine flu epidemic believed to have started in Mexico in April just before Obama's last trip, unbeknownst to the White House. The United States earned huge points with its southern neighbor for not joining the countries banning flights, halting trade and taking other actions that Mexico considered unfairly punitive.

Obama, Calderon and Harper will look for ways to build on that earlier partnership to handle an expected new wave of cases during North America's upcoming flu season. John Brennan, Obama's chief homeland security aide, said it is as important to further link up health officials and ready vaccine and antiviral supplies as it is for the three leaders to publicly reinforce a determination not to panic when cases arise.

"There are people who are going to be getting sick in the fall and die," Brennan said. "We want to make sure that we do everything possible to ensure the continuation of commerce, transportation and trade between the three countries."

America's first- and third-largest trade relationships are with Canada and Mexico. All three are partners in NAFTA, the largest free-trade zone in the world. Closing borders or restricting travel would be very costly for families and businesses on all sides of the borders, an important consideration given the limping economy and the fact that health experts see such actions as pointless in containing the flu's spread.

The U.S. neighbors will want Obama to explain where America's economic recovery is going because both countries saw their own fortunes fall as a result of problems in the U.S. Obama will hear complaints from Calderon and Harper about "Buy American" requirements in the $787 billion economic stimulus package.

The three leaders also are expected to take a joint stand on a recent problem in their hemisphere -- the June coup in Honduras that saw President Manuel Zelaya ousted by the military.

Obama has no separate session with Harper alone. The Canadian leader will see the president on Sept. 16 in Washington.