PHOENIX -- National Guard troops are going to stay at the Mexican border, at least for a little while longer.

The Department of Defense will pick up the $35 million tab to keep 1,200 soldiers in the area through Sept. 30. The original funding was set to run out at the end of this month.

But Capt. Valentine Castillo of the Arizona National Guard said some of the 560 soldiers assigned in this state to Operation Copper Cactus already are gone

"The Guard was in a draw-down process,'' he said, because the original plan had been to have everyone gone by June 30. And Castillo said he cannot disclose how many are left "due to operational security reasons.''

"But what I can tell you is the Arizona National Guard maintains a presence along the Arizona border and it is meeting the mission requirements,'' he said.

Castillo also said that his agency is reviewing applications from soldiers who are not deployed now but are interested in serving through the end of September.

The decision by the Obama administration to keep the soldiers in place comes amid calls by some members of Congress and others for a much more expanded -- and extended -- presence.

John McCain and Jon Kyl, Arizona's two Republican senators, last year called for the president to put 3,000 soldiers along the Southwest border. By April, the pair had doubled that demand, to 6,000, with half of those in Arizona alone, as part of a larger border security proposal.

McCain press aide Brooke Buchanan said her senator welcomes the decision but "believes it's time for Congress to fully fund the McCain-Kyl 10-point border security plan.

But that isn't the direction from the White House.

Matt Chandler, spokesman for the Department of Homeland Security, said the administration sees the Guard soldiers "as a critical bridge,'' there only to fill in while other measures are implemented. That includes additional not just additional Border Patrol officers but also technology to monitor the border with everything from sensors to unmanned aerial vehicles, as well as infrastructure like additional fencing.

Exactly what more will be done, though, remains a bit murkier.

Chandler said his agency, working with other federal departments, "is continuing to explore new options for further strengthening the already unprecedented array of resources deployed at the Southwest border.'' And he said the president wants an "integrated strategy'' to improve border security.

Castillo said many of the Arizona soldiers are part of entry identification teams, set up at locations along the border to monitor for unusual activity. Some also help watch monitors connected to television cameras on towers in the area.

He said, though, they have a support role, reporting what they see to Border Patrol and other agencies.

Chandler said that since the soldiers were deployed all along the border last summer their work has led to apprehension of more than 7,000 illegal immigrants. He also said they have assisted Customs and Border Protection with seizing more than 14,000 pounds of drugs.

The decision to keep the soldiers there through September also has a political component. It comes as the president is pressuring Congress to enact what he calls comprehensive immigration reform, including a path to legal status for the estimated 11 million illegal immigrants already in the country.

That has faced stiff opposition from some members of Congress who say they will not consider such a plan unless and until the border is "secure.'' The president, in turn, has cited statistics which he said shows the border is more secure now than it ever has been.

The Department of Homeland Security says Border Patrol staffing also is better now than it ever has been. There are currently about 20,700 agents, including 3,700 in the Tucson sector alone, compared to 10,000 just seven years ago.

Friday's announcement was not unexpected. Homeland Security Secretary Janet Napolitano had said months ago she planned to move around some existing funds in her own budget. That, however, required approval of key members of Congress.

Chandler said he could not comment about what happened. But Napolitano had made similar requests to revise her spending priorities which were turned down.

Now the Department of Defense will give it a try. Lt. Col. Robert Ditchey said his agency intends to submit a "reprogramming action'' to Congress to free up the $35 million necessary.