Republican presidential candidate Sen. John McCain, R-Ariz. speaks at a press conference as his wife Cindy stands beside him during their visit to the federal police command control in Mexico City, Thursday, July 3, 2008. (AP Photo/Eduardo Verdugo)

MEXICO CITY — From the white roses he laid before a likeness of Mexico's blessed saint, the Virgin of Guadalupe, to the endorsement he gave for an overhaul of U.S. immigration laws, Sen. John McCain used a visit to Mexico on Thursday to appeal to residents of both sides of the border: Mexicans and, more urgently, their voting relatives and other Latinos in the United States.

"We must secure our borders and then we will address the issue of comprehensive immigration reform," McCain said at a news conference in a helicopter hangar that was interrupted by the deafening sound of a heavy rainstorm that made his remarks from the podium unintelligible.

McCain, the presumptive Republican nominee for president, has faced criticism from some of his fellow Republicans for spending time in Colombia and Mexico just as the general election battle heats up, but his campaign officials said the trip could resonate among voters back home by promoting his support of free trade, while highlighting his immigration views during his time in Mexico.

The Arizona senator spoke in the enormous, gleaming command center for Mexico's federal police, which opened last month and serves as a symbol of the country's efforts to crack down on a drug trade that is growing increasingly bloody and threatening to Mexicans.

Despite McCain's lauding of the $400 million in anti-narcotics assistance for Mexico that Congress approved last week, the country remains in the grip of an armed struggle that has thrown large parts of it into lawlessness that has more recently spread to the capital, with the killings of top police commanders.

Mexicans have become inured to reports of daily drug violence, but the day McCain arrived, Wednesday, was particularly gruesome: Four decapitated bodies were found near a threatening message against one of Mexico's top drug lords in the northern city of Culiacan, where the battle over drugs has centered. The police later killed four gunmen in a shootout in Culiacan and recovered an arsenal of weapons in a safe house.

McCain met privately with President Felipe Calderon of Mexico at Los Pinos, the presidential residence. Calderon, even in public, has become a blunt critic of American policies he sees as counter to Mexican interests, strongly criticizing the border wall that has gone up under the Bush administration and the focus on criminalizing migrants.

McCain's previous emphasis on the need for revamping U.S. immigration laws is far more in line with Mexican public opinion than his new emphasis on first cracking down on illegal border crossers.

McCain, who flew to Phoenix on Thursday afternoon, was in Mexico on the third and final day of a Latin American tour intended to promote himself as a seasoned foreign policy hand compared with Illinois Sen. Barack Obama, the presumptive Democratic nominee. The trip also showed McCain in touch with Latinos and Catholics, two key voting blocs in the fall election.