In all, the violence has claimed more than 1,700 civilian lives this year, and federal officials say the killings are on course to top the estimated 1,800 underworld killings last year. Those death tolls compare with 1,304 in 2004 and 1,080 in 2001, these officials say.

Mexico’s law enforcement officials maintain that the violence is a sign that they have made progress dismantling the major organized crime families in the country. The arrests of several drug cartel leaders and their top lieutenants have set off a violent struggle among second-rank mobsters for trade routes, federal prosecutors say. The old order has been fractured, and the remaining drug dealers are killing one another or making new alliances.

“These alliances are happening because none of the organizations can control, on its own, the territory it used to control, and that speaks to the crisis that they are in,” said José Luis Santiago Vasconcelos, the top federal prosecutor for organized crime.

Attorney General Daniel Cabeza de Vaca said a steadily rising tide of drug addiction within Mexico had spurred some of the murders, as dealers fought for local markets. At the same time, more and more honest police officers are trying to enforce the law rather than turn a blind eye to drug traffickers, often paying with their lives, prosecutors say.

But those assessments, other authorities say, are overly rosy and may explain only part of the picture. Some experts say the Mexican police forces, weakened by corruption and cowed by assassinations, are simply not up to the task of countering the underworld feuds unleashed by the arrests of cartel leaders over the last six years.