First, U.S. Border Patrol trucks, tearing down a dirt road and cutting their headlights. Then the helicopter with its deafening blades, dipping and circling, casting spotlights across the water and the mountainside, again and again and again.

On the Mexican side, above the town of Los Algodones, Francisco Lopez watched and listened. For a month, he said, he has been waiting. He sleeps under the shade of trees, scrounges food. Three times he almost crossed.

"They're here day and night," said Lopez, 42, who traveled from the state of Michoacán, Mexico, hoping to reach New York. "When I got here, I was surprised to see so much force on the other side."

The show of force now includes about 6,000 National Guard troops. Two hundred of them from North Carolina started work last week in Arizona. North Carolina's citizen-soldiers, whose home state has one of America's fastest-growing immigrant communities, will reinforce the Border Patrol "perreras" -- dogcatchers.

The deployment is meant to discourage migrants from risking the dash into the United States. The increased security is pushing migrants into remote areas, including harsh desert and mountains, forcing more to use smugglers and leading those who are caught to make repeated attempts that sap their strength and money each time. Many walk for days with little food or water.

"Short-term, you might see more deaths, because they think they can beat the system," said Lt. Col. Randy Powell of Charlotte, commander of the N.C. Guard's 252nd Combine Arms Battalion. Over time, he said, the death toll should drop.

Even before the N.C. Guard arrived, an 11-year-old girl was found in cardiac arrest on a 108-degree day in the remote Tohono O'odham Indian Reservation. The girl, Olivia Nogueda, wearing pink sneakers and traveling with her older sister to Atlanta to meet their parents, was declared dead July 22 at the reservation hospital. Since then, in two counties in eastern Arizona, seven other migrants have died, including two women and a 12-year-old boy.

Last year, as the Border Patrol increased enforcement around urban areas, more than 460 migrants died trying to cross the border, nearly half in Arizona.

"The more difficult you make it for people to cross, the more people will die," said Joseph Nevins, spokesman for Tucson-based No More Deaths, a coalition of humanitarian border groups.

The Border Patrol has increased its efforts to save the people it's hunting. But the Guard's presence will make things more risky, Nevins predicted.

Last week, Ronald Colburn, the Border Patrol's Yuma sector chief, thanked North Carolina's troops: "Psychologically, you have helped us create this 800-pound gorilla," he said.

Border security tightens

Word has spread throughout Mexico: The Guard is coming.

"I read the newspapers," said Hector Encinas, 29, who lives in the Mexican town of San Luis Rio Colorado, just south of San Luis, Ariz. He used to cross routinely to work in the United States, paying $300 a trip. Now the price is $1,500. He used to help others, but no more.

"It's more hard right now," said Encinas, standing in the shade near an opening in the border wall where three Border Patrol trucks were parked. "They got a fence, more soldiers, more Border Patrol."

Of the Guard, he said, "They're cool. They're cool." He knows the troops aren't allowed to make apprehensions, just to call in border agents.

Still, in the more urban Mexican crossing points south of Arizona, something has changed.

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