WASHINGTON, D.C. (AP) - U.S. officials charged with securing Arizona's vulnerable border from illegal immigrant crossings are bracing for what they call a potential new threat - the Minutemen. Camden.

Nearly 500 volunteers have already joined the Minuteman Project, anointing themselves civilian border patrol agents determined to stop the immigration flow that routinely, and easily, seeps past federal authorities. They plan to patrol a 40-mile (64-kilometer) stretch of the southeast Arizona state border throughout April, when the tide of immigrants crossing the U.S.-Mexico border peaks.

"I felt the only way to get something done was to do it yourself," said Jim Gilchrist, a retired accountant and decorated Vietnam War veteran who is helping recruit Minutemen across the country.

"We've been repeatedly accused of being people who are taking the law into our own hands," said Gilchrist, 56, of Aliso Viejo, California. "That is an outright bogus statement. We are going down there to assist law enforcement."

Officials concede the 370-mile (595-kilometer) Arizona border is the most porous stretch on the U.S.-Mexico line. Moreover, recent intelligence show that al-Qaida terrorists are likely to enter the country through the Mexico border, James Loy, the deputy secretary of the Homeland Security Department, said last week.

"Several al-Qaida leaders believe operatives can pay their way into the country through Mexico, and also believe illegal entry is more advantageous than legal entry for operational security reasons," Loy said in written testimony to the Senate Intelligence Committee.

Of the 1.1 million illegal immigrants caught by the U.S. Border Patrol last year, 52 percent crossed into the country at the Arizona border. The agency increased the number of agents in the Tucson sector, which has its largest staff, from 1,700 to 2,100 over the last 18 months.

More will be added to plug the remaining holes, said Customs and Border Protection Commissioner Robert C. Bonner. About 10,000 federal agents now patrol the 2,000-mile (3,220-kilometer) southern border, he said.

Officials fear the Minuteman patrols could cause more trouble than they prevent. At least some of the volunteers plan to arm themselves during the 24-hour desert patrols. Many are untrained and have little or no experience in confronting illegal border crossings.

"Any time there are firearms and you're out in the middle of no-man's land in difficult terrain, it's a dangerous setting," said Bonner, whose agency is keeping a close eye on the Minutemen plans.

"There's a danger that not just illegal migrants might get hurt, but that American citizens might get hurt in this situation," he said.

Civilian patrols are nothing new along the southern border, where crossing the international line is sometimes as easy as stepping over a few rusty strands of barbed wire. But the patrols usually have been small and informal.

The Minuteman Project, because of its scope, may attract what Glenn Spencer, president of the private American Border Patrol, described as camouflage-wearing, weapons-toting hard-liners who might get carried away with their assignments.

"How are they going to keep the nut cases out of there? They can't control that," said Spencer, whose 40-volunteer group, based in Hereford, Arizona, has used unmanned aerial vehicles and other high-tech equipment to track and report the number of border crossings for more than two years.

Gilchrist said the Minutemen are under strict orders to merely identify and follow illegal border crossers and alert federal agents. They should not interact with the immigrants except to offer food, water or medical care. Anyone who steps outside the law will face prosecution, he said.