NACO, MEXICO — The message came on police emergency radio: An army of drug traffickers with machine guns mounted on their pickup trucks was headed toward this town of 5,000 people on the Arizona-Mexico border.
Like a sheriff in a western, police chief and part-time schoolteacher Juan Bracamontes gritted his teeth and assembled his 15 officers, who had nothing better than old .38-caliber revolvers to face off against the enemy.
"Those who want to leave can leave," the chief said. "Those who want to stay and fight, line up behind me and we'll give it to them good."
One officer quit on the spot. The others deployed around the town, but not before taking off their uniforms and abandoning their patrol cars for unmarked vehicles.
In other Mexican towns, local authorities have not shown as much courage in the face of threats from cash-rich drug traffickers. Underarmed, under-prepared and often corrupt, small-town officials and police are the Achilles' heel of President Felipe Calderon's offensive against the nation's drug traffickers.
Calderon has made the battle to rein in Mexico's drug cartels the centerpiece of his presidency, committing large portions of the army and much of the federal police force to the effort.
The cartels have been fighting one another for control of smuggling routes to the United States. The resulting violence claimed more than 2,000 lives last year, and the killings this year have been on a pace to exceed that toll.
In the rural and border areas where smugglers operate, police frequently find themselves on the front line of the drug wars. Arresting a cartel operative might mean death. Even those who agree to protect one band of traffickers risk being attacked by rival gunmen.
Municipal officers account for 60% of the police force in Mexico, with state and federal police making up the rest. Mexican officials and analysts say city police and city officials receive a big share of the estimated $3 billion that drug traffickers pay in bribes each year.
Officials at Mexico's Public Safety Secretariat estimate that traffickers pay police an average monthly bribe of $500 to $600, roughly equal to a starting officer's monthly salary in towns such as Naco and neighboring Cananea.
"The training these officers receive is very precarious, as is their pay," said Raul Benitez, a professor at American University in Washington and a specialist in Mexican security issues. In many towns, Benitez said, the only requirement for becoming a police officer is being a friend of the mayor: The police force is a prime political plum.
These undertrained officers face an increasingly sophisticated enemy, as Mexico's drug cartels form small armies in which many of the "troops" have at least some military-style training.
Two days before the report of a "caravan of death" headed for Naco, as many as 50 armed men attacked Cananea. Five municipal officers were kidnapped and killed in the May 16 incident. Within hours, half of the 48-officer Cananea police force had turned in their guns and quit.
"We have no protection," several Cananea officers told reporters gathered around the town's police station. With allegations of links to traffickers swirling around the force, eight officers were fired, as was the police chief.
"On the one side organized crime is killing police officers, and on the other side the government is investigating and firing them," said Jose Arturo Yanez, a researcher at the Professional Police Training Institute in Mexico City. "No one is protecting them."
Security officials have resigned or been fired en masse in at least 18 states in nearly every region of Mexico.
Dozens have walked away from their jobs. A few have fled in the face of arrest warrants. Others, such as Orlando Valencia of Cananea, disappear from their offices.
Valencia was both the mayor's spokesman and the city emergency coordinator. In late May, he disappeared, and officials announced that they were seeking his arrest on suspicion of aiding drug traffickers in their escape after the attack on Cananea.
Even for those brave enough to serve in the country's most dangerous towns, discretion is usually the better part of valor. One high-ranking police official in a town in Zacatecas state explained the advice he gives his officers to keep them safe:
"I told them that if they see something suspicious, they should withdraw," said the official, who asked not to be named. "It doesn't matter what it is, just withdraw.... These people are well-armed and we just have the basics."
After an encounter with suspected cartel hit men, many officers in his town received telephone death threats. A good chunk of the force resigned.
"I don't know why they quit," the official said. "And you know what? I don't care."