The troops have been deployed in "Operation Jump Start," which over the next two years will support U.S. Customs and Border Protection as it hires and trains 6,000 new Border Patrol agents.
The Air Force Times reported Tuesday that the troops will free up more Border Patrol agents to return to law enforcement duties along the frontier.
The National Guard Bureau said Monday that 6,199 troops were serving along the border. The announcement came the day before an Aug. 1 deadline given to the Guard to have up to 6,000 soldiers and airmen deploy to the four states.
Operation Jump Start is part of an immigration reform package announced in May by President George W. Bush. It also involves constructing a fence along the U.S.-Mexican border.
A memorandum of agreement between the Department of Defense and the governors of the four states defines the terms of the deployment.