President Obama, after meeting Thursday with Mexico's president, signaled he is backing away from his pledge to renew the U.S. ban on assault weapons but still wishes to stop the cross-border flow of guns that wind up in the arsenals of drug cartels.

The military-style assault weapon ban expired in 2004, and Obama faced an uphill political battle in winning a renewal of the law, which is unpopular in key political states and among Republicans and some conservative Democrats.

Obama said Thursday he preferred to focus on enforcing existing laws to keep assault weapons out of Mexico, rather than trying to renew the U.S. ban on the weapons.

"We are absolutely committed to working in partnership with Mexico to make sure we are dealing with this scourge on both sides of the border," Obama said at a news conference with Calderon outlining their strategy.

"You can't fight this war with just one hand," he said. "You can't have Mexico making an effort and the United States not making an effort."

Obama, on his first trip to the region as president, said that he will push the U.S. Senate to ratify an inter-American arms trafficking treaty designed to curb the flow of guns and ammunition to drug cartels and other armed groups in the hemisphere. The regional treaty, adopted by the Organization of American States, was signed by former President Bill Clinton in 1997 but never ratified by the Senate.

Obama made the announcement after meeting Thursday afternoon with Calderon. The meeting is the centerpiece of Obama's visit to Mexico, whose government is engaged in a broad war against heavily armed drug cartels now threatening the integrity of the state.

The U.S. ban on military-style assault weapons became law during the Clinton administration in 1994 and contributed to the Democrats' loss of Congress that year. It expired under the Bush administration in 2004. When Attorney General Eric Holder raised the idea of reinstituting the ban this year, opposition from Democrats and Republicans emerged quickly.

"We know that it is a politically delicate topic because Americans truly cherish their constitutional rights," Calderon said.

During his stop in Mexico City on Thursday, Obama emphasized cross-border cooperation and focused on clean energy, but the economic crisis and the bloody drug trade have set the tone.

Calderon greeted Obama to the presidential residence, Los Pinos, with an acknowledgment of the costs "to turn Mexico into a safer country." Citing a visit a half-century ago by President John F. Kennedy, Calderon called for a new era of cooperation between the neighboring countries.

"In order for Mexico to grow and prosper, Mexico needs the United States' investments, and the United States of America needs the strength of the Mexican labor force," Calderon said.

Obama echoed Caledron's call for cooperation in his brief statements and said it was more important than ever for the two countries to work together in grappling with the drug war.

"At a time when the Mexican government has so courageously taken on the drug cartels that have plagued both sides of the border, it is absolutely critical that the United States joins as a full partner in dealing with this issue," he said.

The escalating drug war in Mexico is spilling into the United States, and confronting Obama with a foreign crisis much closer than North Korea or Afghanistan. Mexico is the main hub for cocaine and other drugs entering the U.S.; the United States is the primary source of guns used in Mexico's drug-related killings. 

Homeland Security Secretary Janet Napolitano told FOX News on Thursday the meetings with Mexican officials are not about pointing fingers but solving problems. 

"So on the U.S. side we want to make sure that spillover violence doesn't occur. But we also want to assist Mexico in its own efforts to make sure -- to clamp down on these cartels; to do what they can to break them up," she said. "Well, you've got to deal with several things simultaneously. One is, again, working with Mexico to increase their own law enforcement capacity. Two is, increasing our own resources at the border itself."

Calderon's aggressive stand against drug cartels has won him the aid of the United States and the prominent political backing of Obama -- never as evident as on Thursday, when he left Washington to fly to the Mexican capital and stand with Calderon on his own turf. 

Obama's overnight Mexican stop came on the way to the Summit of the Americas in the two-island Caribbean nation of Trinidad and Tobago, where he hopes to set a new tone for relations with Latin America

"We will renew and sustain a broader partnership between the United States and the hemisphere on behalf of our common prosperity and our common security," he wrote in an opinion column printed in a dozen newspapers throughout the region. 

In the past, Obama said, America has been "too easily distracted by other priorities" while leaders throughout the Americas have been "mired in the old debates of the past." 

More than 10,000 people have been killed in Mexico in drug-related violence since Calderon's stepped-up effort against the cartels began in 2006. The State Department says contract killings and kidnappings on U.S. soil, carried out by Mexican drug cartels, are on the rise too. 

A U.S. military report just five months ago raised the specter of Mexico collapsing into a failed state with its government under siege by gangs and drug cartels. It named only one other country in such a worst-case scenario: Pakistan. The assertion incensed Mexican officials; Obama's team disavowed it. 

Indeed, the Obama administration has gone the other direction, showering attention on Mexico. 

Secretary of State Hillary Rodham Clinton said in Mexico City that the U.S. shared responsibility for the drug war. She said America's "insatiable demand" for illegal drugs fueled the trade and that the U.S. had an "inability" to stop weapons from being smuggled south. 

Obama has dispatched hundreds of federal agents, along with high-tech surveillance gear and drug-sniffing dogs, to the Southwest to help Mexico fight drug cartels. He sent Congress a war-spending request that made room for $350 million for security along the U.S.-Mexico border. He added three Mexican organizations to a list of suspected international drug kingpins. 

He dispatched three Cabinet secretaries to Mexico. And he just named a "border czar." 

FOX News' Mike Emanuel and The Associated Press contributed to this report.