More than 6,000 National Guard troops have been assigned to southwestern border states by the government's Aug. 1 deadline — though only about half of them are on duty along the border, the Guard said Monday.

Guard officials said 6,199 troops were somewhere in the four southwestern border states, with many still in training. Col. Mark Allen, a spokesman for the National Guard Bureau, said 2,000 to 3,000 were on the border, most searching for illegal activity.

The Guard never intended to have 6,000 troops "with their toes on the border," Allen said. The number will fluctuate depending on Border Patrol requests, he said.

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Bush's plan for curbing illegal immigration, announced in May, called for as many as 6,000 troops on the border. The Guard said they would be there by Aug. 1.

California has assigned more than 1,200 troops, Guard spokesman Maj. Dan Markert said Monday. About half will be at the border looking for illegal activity; the other half will be in support roles ranging from plumbers to office workers.

Most of the troops in Arizona are working at Border Patrol stations doing such jobs as communications and administrative support and vehicle repairs, Maj. Paul Aguirre said. Some are assigned to military bases to receive incoming troops.

In New Mexico, troops are helping spot illegal immigrants, building vehicle barriers and working in office positions, Agent Patrick Berry said. Soldiers near El Paso, Texas, were doing video surveillance and tending to horses, Border Patrol spokesman Doug Mosier said.

The Border Patrol credits the Guard with helping arrest 2,296 illegal immigrants, and seizing 14,496 pounds of marijuana and 200 pounds of cocaine, said patrol spokesman Mario Martinez.

Last week, Border Patrol Chief David Aguilar said that in the 69 days after Bush's announcement the agency registered a 45 percent drop in arrests along the U.S.-Mexican border, compared with the 69 days before.

But T.J. Bonner, who heads a union representing Border Patrol agents, credited a severe summer heat wave with the drop.

"It's normal for traffic to decline when the heat hits triple digits," said Bonner, president of the National Border Patrol Council.