SAN DIEGO – No boots were seen tromping in the desert sand on Sunday. No commanders were heard barking out orders to their troops. The National Guard, which officials had announced would turn out en masse along the U.S.-Mexico border over the weekend for sentry duty, was nowhere to be found.

It turns out it will take weeks longer to select, screen and train the 1,200 National Guard troops the Obama administration had said would be deployed on Aug. 1 along the border from California to Texas.

Administration officials explained that the announced date was always a starting point, the beginning of the process of deployment and not the day camouflaged soldiers would begin amassing at the boundary line with their automatic weapons, high-powered binoculars and filled-up canteens.

"Full deployment will take place over succeeding weeks," Janet Napolitano, the secretary of homeland security, said in an interview. "It won’t be 100 percent showing up all of a sudden."

Once they arrive in the weeks and months to come, the troops will do what the thousands deployed during the Bush administration did: aid Border Patrol agents but not carry out direct law enforcement functions, Gen. Craig McKinley, chief of the National Guard Bureau at the Pentagon, said at a recent briefing. Instead of capturing migrants and traffickers, the troops will serve as lookouts, assess intelligence and carry out other support roles, McKinley said. They will join several hundred National Guard troops already there helping to stop drug trafficking.

Having the additional boots at the border – divvied up in Arizona, California, New Mexico and Texas – will free up the federal law enforcement officials who are focused on drugs and illegal immigration, Napolitano said. The yearlong supplemental staffing will give the administration time to hire additional civilian personnel, she said.

Of course, there is a political dimension to the deployment, which comes as the Obama administration faces fierce criticism, particularly in Arizona, for not doing enough to seal off the borders from illegal immigrants and drug smugglers.

"It’s for show," said Tony Payan, a political science professor at the University of Texas at El Paso who studies the border. "It’s the kind of climate we live in today, using war lingo, military jargon, using the National Guard, it seems like we’re being more effective, being serious. It sounds impressive, but it’s just 1,200 people."

Doris Meissner, a fellow at the Migration Policy Institute and an immigration commissioner in the Clinton administration, said the number of border guards, no matter how high or which agency they belonged to, would never truly solve the problem of illegal immigration.

"During my time, 10,000 Border Patrol agents was considered the magic number," she said. "Then it became 20,000. If it grew to 25,000 or 35,000 or even 50,000, that would be marginally better, no doubt. But illegal immigration is an economic issue. It’s a market phenomenon. Legislation that deals with the problem as a whole is the only real solution."

Jay Ahern, former commissioner of Customs and Border Protection, said he was not surprised that Aug. 1 came without any visible troops.

"You don’t just turn a switch and have this happen overnight," said Ahern, who was involved in Operation Jump Start, President George W. Bush’s deployment of thousands of National Guard troops to the border from 2006 to 2008. "And these are not going to be people visible at our points of entry. They will be in remote areas and in support roles."