Phoenix ? Fifty-five National Guard members from Utah arrived in Yuma on Saturday afternoon – the first troops to be sent to the Arizona-Mexico border in a new crackdown on illegal immigration.

The Utah troops had been scheduled to work on fences and other projects as part of the Guard’s long-standing efforts at the Arizona border, officials had said as late as Wednesday. But their mission has since been folded into President Bush’s plan to send up to 6,000 National Guard troops to the four southern border states to supplement federal immigration agents.

The Utah troops got word of the change Friday from Guard officials in Washington, D.C., said Maj. Hank McIntire, a spokesman for the Utah National Guard. They are scheduled to be briefed on their mission Sunday and start field work as early as Monday, he said.

Under the president’s plan, troops will perform support duties to allow federal authorities to focus on border security. They won’t perform law enforcement duties.

The Utah troops, who will not carry weapons, will be in Yuma for two weeks to install improved lighting at a border crossing, extend an existing border fence and build a road, McIntire said.

The projects will be done in the area of San Luis, Ariz., a town 25 miles south of Yuma with a fortified stretch of border with Mexico.

The town is part of the nation’s busiest U.S. Border Patrol station, in a state that is the nation’s busiest illegal entry point.