The officers and agents on Wednesday raced into the ramshackle house with their assault rifles ready. They searched for a bag of white powder - an unknown chemical with unknown consequences. It could have been anthrax. It could have been deadly.

This time, the powder was harmless, part of a weapons of mass destruction training session in Bayview sponsored by U.S. Immigration and Customs Enforcement (ICE). Local and federal law enforcement agencies are participating in the weeklong training, which focuses primarily on the threat of terrorism.

Along the border, officials said, that threat is particularly real.

"The easiest targets for terrorists are the ones who are least prepared," said John Chambers, chief of police at Indian Lake. The training sessions are taking place in Indian Lake and Bayview. They began on Monday and will run until Friday.

The training is being paid for by a government grant, which provided experienced instructors who explained the impact of chemical, biological and radiological weapons. During lectures, officers from the San Benito Police Department, the McAllen Independent School District police force and federal agents learned about the history of such weapons and how to protect themselves during dangerous encounters.

One instructor pointed to a photo of a drop of nerve agent on the face of a penny.

"If I put that much on all you guys, at least 50 percent of you are going to be dead," he said.

On Wednesday, 30 officers and agents participated in numerous simulations, shooting rubber bullets at actors who were posing as terrorists. They wore gas masks and protective gear - just as they would have to in the case of a terrorist act.

"These guys are getting a lot out of this," Chambers said. "It's necessary information that they've never heard before."

Local police departments interested in a similar training are encouraged to contact John Chambers at (956) 233-8559.