“It’s going to complicate the scenario of civil and human rights at the border,” said Fernando Garcia, executive director of the Border Network for Human Rights. “Border Patrol agents have to go through a number of certifications in academy and post-academy training on immigration law, on civil rights law. Now you’re talking about putting in soldiers doing that kind of work. Legally, it’s going to be a disaster if they start enforcing criminal, civil or immigration laws.”

Mr. Perry and Maj. Gen. John F. Nichols, the adjutant general of the Texas National Guard, emphasized the supporting role the 1,000 troops would play. They said the troops were needed because Mexican drug cartels and other criminal organizations were taking advantage of the federal government’s focus on the wave of Central American immigration that has flooded the border in recent months.

General Nichols said the troops would undergo training, and he described their mission as “referring and deterring” — having their presence on the border act as a deterrent and referring people who they suspect are illegal immigrants to state law enforcement officers.