That, however, hasn't stopped Mexicans from acquiring firearms. The country is awash in illegal guns, many of them assault weapons in the hands of merciless criminal gangs. President Felipe Calderon says authorities have seized more than 140,000 weapons since he came to office in late 2006. Many of them, Mexican officials assert, were purchased in the United States.

Nothing highlights the cultural and legal differences between Mexico and the United States as starkly as Mexico's lone gun shop, whose ponderous name is the Directorate of Arms and Munitions Sales.

In contrast, the four U.S. border states - California, Arizona, New Mexico and Texas - have 20,834 firearms dealers licensed by the U.S. government, according to Marc Willis, a spokesman for the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives.

In the gun shop here, soldiers keep a wary eye on customers as they pass through a metal detector. Once inside, clients seeking protection for their homes are each permitted to buy one small-caliber handgun. They also can obtain 200 rounds of ammunition a year.

"Normally, we have 70 or 100 visitors a day," army Col. Raul Manzano Velez said as he took a visitor past rows of wooden cabinets displaying Belgian-, German-, Turkish- and U.S.-made handguns and single-shot hunting rifles.

The shop's existence is unknown to many citizens. "The federal firearms law forbids us from advertising so as not to promote rampant gun buying," Manzano said.

The differences between U.S. and Mexican gun laws date to the days when founding fathers north of the border saw armed militias as a necessity to guarantee freedom while Spanish rulers south of the border saw guns as a threat.

"The last thing the Spanish grandees or the hacendados (large landowners) wanted was people running around with guns," said Ray Walser, a senior policy analyst on Latin America at the Heritage Foundation, a conservative research center in Washington.

"The principle of defense is pretty much ingrained in our culture," Walser said of the United States. "In Mexico, they say, 'The state will defend you.' But it doesn't defend you. ... So we end up trading invectives at each other."

Calderon, usually with fury in his voice, has lashed out at what he calls lax U.S. gun laws, most recently on Feb. 16 as he stood near a billboard erected in Ciudad Juarez that said, "No More Weapons!" The sign faces the U.S. border.

Calderon said organized crime in Mexico had grown stronger due to "unlimited access to high-powered weapons that are sold freely and indiscriminately in the United States of America."

Despite the rigor of Mexico's gun laws, its murder rate of 18 per 100,000 people is more than triple the United States' rate of five per 100,000. Nearly all homicides in Mexico occur with firearms.

Mexico once had a few private gun shops but the last one was abolished in 1995, leaving business to the army store. Profits go to the national treasury.

Obtaining a gun involves first getting a permit. Requirements include an official photo ID, proof of residency and employment, a document showing fulfillment of military service and a declaration of a clean criminal record.

"When you have all these documents, you take them to the federal firearms registry, and within five to 10 working days you get the license," Manzano said.

For those seeking guns for home protection, the law requires that the firearms never leave the permit holders' primary residences. The firearm can be from .22 to .380 caliber. It can be a pistol or a revolver, but can't be a rifle. Only a single gun is allowed.

A different permit is given to marksmen and hunters, allowing them each to own up to nine single-shot rifles or shotguns and one small-caliber handgun. Mexico has 89 gun and hunting clubs and 20 government offices that sell hunting licenses.

Mexico's 289 private security companies also have a different regimen: They can buy semiautomatic weapons or higher-caliber pistols and revolvers.

No matter how far buyers live from Mexico City, they must travel to the capital to obtain the licenses, give fingerprints and purchase the weapons.

Manzano acknowledged that the system is "very inconvenient" for the buyer, especially given the underground market for weapons.

"There is an enormous black market in the country. You can buy any weapon without any problem on the street. That is the reality in Mexico," he said.

A client in the army gun store, lawyer Carlos Davalos, said Mexico's strict gun laws hadn't stopped criminals from obtaining weapons.

"There isn't really control over guns in Mexico," he said.

He scoffed at the legal restrictions on the caliber of handguns that citizens are allowed to have.

"If somebody breaks into your house and instead of a .380, you have a (more powerful) .357 Magnum and you kill him, guess what? You save your life but you are going to jail," Davalos said.

Another man in the gun store, Santiago Mac Gregor, a 29-year-old founder of a target shooting business, Shooting Sports Mexico, also criticized the firearms regulation.

"Who gives them the power to tell me what caliber I can buy?" Mac Gregor said in English. "What happens if you desperately need a gun to protect your house? They tell you that you can only have one gun, 200 rounds and you can't take it out of your house. It's silly. So you go to the black market."

Jose Luis Gonzalez, the head of El Aguila Hunting Club in the state of Mexico, said members of his club didn't object to limits on rifle purchases as much as they griped about red tape that entangled the quest for permits and how hunts took place.

"To get this letter declaring that you have no criminal record is a real headache. It took me two months," Gonzalez said.

Because hunting for white-tailed deer usually occurs on private communal lands known as ejidos, community members set the prices for obligatory services for hunters, he said, and dictate conditions on how the hunts can occur.

"They put bait out for the deer at 25 or 30 meters, and you assassinate the animal," Gonzalez said. "This is not hunting."