* Mexican officers already in police custody * Authorities keep open mind to drug links * Incident was major embarrassment for Calderon By Gabriel Stargardter MEXICO CITY, Nov 9 (Reuters) - Mexico charged 14 federal police officers on Friday with the attempted murder of two CIA operatives after the U.S. agents' vehicle was sprayed with bullets in a brazen daylight attack that security officials suspect was ordered by a drug cartel. The ambush was initially blamed on a case of mistaken identity, but Mexican security sources said the fact that police officers used AK47 assault rifles and were not wearing uniforms suggested a gang-orchestrated hit. The August incident, in which the CIA operatives tried to escape the hail of semi-automatic gunfire in a dramatic car chase, was a major embarrassment for the government of outgoing President Felipe Calderon, who has staked his reputation on taming the cartels. The CIA officers' diplomatic vehicle was peppered with 152 bullet holes. Their injuries were not life-threatening and they were quickly moved out of the country. The attorney general's office said it charged the 14 federal police officers with attempted murder. "We're not discounting any theory, including that they could be involved with organized crime," an official said on condition of anonymity. The 14 police officers come from the southern Mexico City district of Tlalpan and were already in police custody, the statement said. Drug cartels often take advantage of low pay for Mexican police to infiltrate their ranks and put officers on the payroll. "The reputation of our police was already at rock bottom, and this doesn't help one bit," said Maximiliano Moyano, a criminal lawyer who works on police corruption cases. The incident was the worst attack against U.S. officials in Mexico since drug-gang assailants killed a U.S. immigration agent and wounded his colleague in a highway attack in early 2011. The August attack took place near the town of Tres Marias on a road south of Mexico City, and came as increased cooperation between U.S. and Mexican forces seemed to be yielding results in Calderon's six-year offensive against the bloody cartels. NEW PRESIDENT INHERITING 'VERY PROBLEMATIC SITUATION' Since 2009, government troops have caught or killed more than 20 major drug lords. But that has led to cartel infighting and fragmentation, and recent drug war victories have been offset by humiliating cases of corruption and bungled operations. A June shootout between federal police and corrupt fellow officers at Mexico City's airport killed three officers. That was followed by last month's killing of Zetas cartel leader Heriberto Lazcano, a significant victory for Calderon that was undermined by the late-night theft of Lazcano's body from a funeral home, fueling rumors the kingpin was still alive. About 60,000 people have died in drug violence during Calderon's term, and the bloodshed hurt his party's candidate in the presidential election in July. President-elect Enrique Pena Nieto, who takes office on Dec. 1, says his priority will be to reduce violence and focus first on tackling crimes like extortion and kidnapping. But Pena Nieto, who is leading the Institutional Revolutionary Party, or PRI, back into power after a 12-year hiatus, has rejected negotiating with the gangs, mindful of the PRI's past reputation for cutting deals. "Calderon hands over to Pena Nieto a very problematic situation, but with one main advantage: it seems that violence at the national level is starting to trend downwards," said Eduardo Guerrero, a security analyst with Lantia Consultores in Mexico City. Despite the Tres Marias attack and a new government taking office, analysts do not expect drug-fighting collaboration between Mexico City and Washington to change drastically. "Mexico's relationship with the United States is very institutionalized," said Alejandro Hope, a security analyst at the Mexican Institute for Competitiveness.