Participants in the Minuteman Project spotted the migrants Saturday near Naco as the volunteers were surveying the border to familiarize themselves with the area. When agents arrived, they apprehended 18 people, Border Patrol spokesman Andy Adame said.

''You observe them, report them and get out of the way,'' said Mike McGarry, a spokesman for the project, which begins toay and is to continue for a month.

The volunteers reported another border crosser after he wandered onto the campus of a Bible college near the community of Palominas, where about 100 Minuteman participants were staying.

The man walked in and said he needed food and water. Volunteers helped him and notified federal agents, who picked him up, McGarry said.

The man was weary from traveling but didn't need medical attention, Adame said.

''It's not uncommon to have aliens that have had enough,'' Adame said. ''They'll walk up to someone's house and ask them to call us. They're waiting on the porch when we arrive.''

Minuteman volunteers planned to start regular patrols today, fanning out across 23 miles of the San Pedro Valley to watch the border and report any illegal activity to federal agents.

It's an exercise some law enforcement authorities and others fear could lead to vigilante violence.