SAN LUIS - Military bulldozers, road graders and other heavy equipment rumbled along the Mexican border early Monday as more than 50 National Guardsmen from Utah became the first unit to get to work under President Bush's crackdown on illegal immigration.

The soldiers with the 116th Construction Support Equipment Company rolled out of bed at 3:45 a.m., and will hit their work sites by 5:30 a.m. during their two weeks of duty. They will improve a dirt road running parallel along the border, fill in gaps in fortified fencing and run wiring for new lighting to help the Border Patrol spot illegal immigrants trying to come across.

"It's exciting to do something that's relevant to the safety of the United States," said Capt. Talon Greeff, the unit's commander. "There is a sense of excitement when you are doing something real-world."

The goal is to strengthen the border and free up border agents to catch illegal immigrants.

The guardsmen are unarmed and wearing hardhats instead of Kevlar helmets - "we do not want to appear as if we're militarizing the border," Greeff said. They will not perform any law enforcement duties.

And not having to worry about their weapons while working is nice, he said, though acknowledging that "it makes me nervous to know there might be people that are not happy about our presence on the other side of the border and I just worry about my soldiers."

The troops arrived in Yuma on Saturday and were briefed Sunday on their mission and given tips on how to survive the triple-digit heat of the Arizona desert.

Under Bush's plan, up to 6,000 National Guardsmen will be sent to the four southern border states. Officials say 300 Guardsmen from Arizona are expected to begin arriving at the state's border in mid-June.

The Utah unit is working along the border at San Luis, 25 miles south of Yuma. Two sets of barriers run along the border west of the San Luis port of entry: a 12-foot corrugated-metal fence and, about 50 yards to the north, an 8-foot chain-link fence topped with barbed wire. Surveillance cameras are mounted on towers, and stadium lights help agents spot people trying to slip across at night.

Most of the 11 soldiers assigned to operate the heavy equipment have full-time jobs in the construction business in Utah. They would normally be pulling two weeks of training duty at this time of year anyway, and had already been set to work on the border for their training.

Now they will widen and upgrade the sandy track used by the Border Patrol - compact it, raise it and top it with several inches of gravel so agents can get to hot spots faster.

"They asked our unit to come out and help with the program with Arizona, help the security force. It's an honor for me to come out here," said Sgt. 1st Class James Colledge, a 52-year-old truck driver from West Valley, Utah. "They all feel pretty privileged to be out here, as the first group."

Asked how he was handling the triple-digit heat, Sgt. Jody Cloward of Cantaquin, Utah, said he was surprised to learn that his annual two-week training session had been rolled into the president's border-security plans.

As for the weather, Cloward said, with a chuckle, "It's actually quite nice. A little warm, but ..." The temperature in Yuma topped out at 110 degrees Sunday and was expected to be nearly as hot Monday.

In San Luis, some residents were pleased with the guard's presence.

Raymond Ruiz, a clerk at Charles and Frank Auto Parts, said the response was long overdue.

"I think we need it, because besides illegal people coming across, I know there's drugs and you never know, maybe some terrorists one of these days," Ruiz said. "I just hope that they do it right. I know it'll help. It'll probably take a lot more than this, but it's a good beginning."

Others were leery, worried that legal border crossers would stop shopping.

At Alex Furniture employee Israel Escobar said the Guard's presence "scares the people. No one wants to buy in the U.S."

But his co-worker, Israel Torres, disagreed.

"It's OK. It's right, because it means more security in the houses," Torres said. "I live next to the border, and I'm afraid."