President Obama has authorized the call-up of as many as 1,200 National Guard troops along the U.S. border with Mexico to assist with border protection and enforcement activities there, officials say.
The president, who alone cannot formally authorize deployment of the forces, is expected to request $500 million in supplemental funds from Congress to make a state governor's decision to deploy troops financially possible.
The troops, expected to be spread along the southern border of all four southwestern states, would largely assist border patrol agents and local law enforcement by providing intelligence and intelligence analysis, surveillance and reconnaissance support, and the ability to train additional Customs and Border Protection agents, sources say.
Deployment of National Guard troops would "provide immediate enhancement to the unprecedented and ongoing border protection and security efforts that over the last 16 months have increased pressure on illegal trafficking organizations," one administration official said.
Today's announcement comes one week after a U.S. state dinner honoring Mexican President Felipe Calderon at which Obama promised to "continue to do what's necessary to secure our shared border."
Arizona Gov. Jan Brewer today praised Obama's decision saying in a statement, "with the accountability of this election year, I am pleased and grateful that at long last there has been a partial response from the Obama Administration to my demands that Washington do its job."
Members of Arizona's congressional delegation also supported sending additional troops to the border.
"The White House is doing the right thing," said Rep. Gabrielle Giffords, D-Ariz., who began calling on the president to deploy the National Guard in March. "Arizonans know that more boots on the ground means a safer and more secure border. Washington heard our message."
But for some Arizonans, including Republican Sen. John McCain, 1,200 troops is insufficient.
"It's simply not enough," he said during debate on the Senate floor this afternoon during which he described Arizonans who live in fear of cross-border violence from drug lords. "We need 6,000."
McCain and fellow Arizona GOP Sen. Jon Kyl are calling on Obama to visit the Mexico-U.S. border in their state to "personally witness the need for additional personnel, technology and infrastructure necessary to secure the border."
Earlier this month they wrote a letter to Obama urging him to authorize deployment of Guard troops.
"The governors of Arizona and Texas have requested the deployment of the National Guard, and the governor of New Mexico has deployed his state's National Guard to the border," they wrote on May 17. "We again urge you to deploy at least 6,000 National Guardsmen to protect our southern border, with 3,000 of these troops focused on the Arizona-Mexican border."
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Arizona Democrat Rep. Ann Kirkpatrick, who sits on the House Homeland Security Committee, said the president's move was a step forward but that a long-term, sustainable solution for a secure border would involve hiring more border patrol agents.
"I introduced legislation calling for 3,500 new USBP agents to be hired, trained and deployed at the U.S.-Mexican border by the end of next year," she said. "That plan needs to be enacted as soon as possible."
President George W. Bush made a similar order in 2006 to send National Guard troops to assist Border Patrol, but they served primarily in a support role.
In the past few months, aggressive Mexican drug smugglers and migrants have harassed residents of Cochise County in Arizona's southeast corner, burglarizing homes and taking food and clothing, local law enforcement officials say.
The U.S. Border Patrol says apprehensions along the Arizona-Mexico frontier are up 6 percent from October to April.
But while several violent high-profile incidents in the Tucson, Arizona, sector have gained national attention and colored political rhetoric, an ABC News analysis of immigration and crime data, combined with interviews with law enforcement officials, shows that reported violence and crime on the U.S. side of the 2,000-mile border with Mexico are generally on the decline.
ABC News' Sunlen Miller, Luis Martinez and Z. Byron Wolf contributed to this report.