(Adds three dead in Tabasco, details)

By Greg Brosnan

APATZINGAN, Mexico, May 9 (Reuters) - Heavily armed troops scoured one of the most violent towns in Mexico on Wednesday, combing unpaved streets in convoys in search of drug traffickers who have launched increasingly bold attacks on security forces.

Backed by Humvee vehicles, dozens of soldiers fanned out on foot in a slum in the western town of Apatzingan, where nine people have died in the last few days in clashes between the army and drug hitmen.

Residents peered from doorways at otherwise deserted streets as edgy soldiers, many wearing black ski masks to hide their identities despite searing heat, ordered occupants out of houses and searched them for drugs and guns.

"I'm scared, but where else can we go?" said construction worker Jose Luis Gonzalez, emerging from his house. Soldiers with sniper rifles scanned the skyline but no arrests were made.

Mexican President Felipe Calderon has sent thousands of troops and federal police to tackle drug cartels across Mexico, but the increased firepower has failed to contain the violence, including a recent wave of attacks on senior officers.

Soldiers supported by helicopters killed four drug gang members in a two-hour shootout in Apatzingan on Monday.

Last week in a nearby town, cartel members killed five soldiers in a brazen attack that was one of the heaviest blows to the military's anti-drugs drive.

Apatzingan lies in the Pacific Coast state of Michoacan and is a center for methamphetamine production and cocaine trafficking. The army is trying to squash two cartels fighting each other over routes and territory.

BITTER FIGHT

Nationwide, the Gulf Cartel based in northeastern Mexico is fighting an alliance of smugglers from Sinaloa state, headed by Mexico's most-wanted man, Joaquin "Shorty" Guzman.

Three people were found dead in a sewage canal in the state of Tabasco, their bodies bearing the hallmarks of drug executions. The victims had their hands and feet bound and suffered close-range gunshot wounds to the back of the heads.

The Milenio gang, local allies of fugitive Guzman, are believed to be behind the recent clashes with the army in and around Apatzingan.

Human rights officials warn that the army offensive, which is also heavy in states on the U.S. border, could lead to abuses by heavy-handed troops, but many of the public support it.

"I think there is no other force at the moment that can carry out this task," Michoacan Gov. Lazaro Cardenas said of the army.

Drug gunmen disguised as federal agents shot dead the head of police in a state capital near the beach resort of Acapulco on Wednesday, adding to nearly 800 killings so far this year.

Dressed in black fatigues, they shot police chief Artemio Mejia in Guerrero's dusty state capital Chilpancingo after he got out of his pickup truck to question them.

Some 2,000 people died in narcotics-related violence in Mexico in 2006.

Soldiers killed a suspected drug gunman at an army checkpoint outside the southern beach resort of Huatulco early on Wednesday, newspapers reported.

(Additional reporting by Gerardo Torres in Chilpancingo, Miguel Gutierrez and Noel Randewich in Mexico City)

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