By Jon Herskovitz

BASTROP, Texas, July 12 (Reuters) - To hear the conspiracy theorists tell it, a labyrinth of tunnels is being built under Walmart stores for military attacks on civilians, and an orchestrated financial crisis will lead to martial law, U.S. troops patrolling chaotic streets, and a dictatorship under President Barack Obama.

These and similar tales have gained currency in recent months among a small but powerful group of anti-government Texas voters in the run-up to planned military training drills in the West and Southwest, including in the Lone Star state.

While such views represent the fringes of American political opinion, they reflect a broader suspicion of the federal government that has run deep in Texas for years.

The U.S. Army Special Operations Command exercise, called Jade Helm 15, has brought these fears to a crescendo, particularly in Bastrop. Some of the exercises, scheduled from July 15 to Sept. 15, will be held in this city located east of Austin.

At an April town hall meeting in Bastrop, attendees peppered a military spokesman with pointed questions, including: "Are you planning on detaining or rounding up any American citizens?"

Rosalie Howerton, a 74-year-old retired nurse from Tyler, Texas, wrote the governor to say she was worried about the drills.

"I've gotten to the point where I don't trust my government," she said. "I don't trust Obama. I think he is looking toward calling martial law to stop the next election from taking place."

In an online comment about Jade Helm, Bastrop resident Josh Munyon wrote: "It's something that the rest of the country should be worried about. They already have FEMA trains that oddly enough look like the trains that the Nazis used in ww2."

One particular sticking point has been an Army map that lists Texas as "hostile" territory.

"Such labeling tends to make people who have grown leery of federal government overreach become suspicious of whether their big brother government anticipates certain states may start another civil war or be overtaken by foreign radical Islamist elements which have been reported to be just across our border," Louie Gohmert, a Republican congressman from Texas, said recently in a statement.

The Texas Republican Party platform has long reflected concerns over federal and international overreach, with calls for a U.S. withdrawal from the United Nations and the elimination of the Federal Reserve.

When a U.N. agency named the Alamo, the location of a famed 1836 battle in the fight for Texas Independence, a World Heritage Site earlier this month, some Texans saw the move as a prelude to an international takeover.