WASHINGTON (Reuters) - President Barack Obama will seek $500 million for security and send up to 1,200 National Guard troops to the U.S.-Mexican border, an administration official said on Tuesday, after demands from both Republicans and Democrats for more federal resources along the frontier.

A view of the U.S.-Mexico border fence in Nogales, Arizona is pictured in this photo taken April 28, 2010. REUTERS/John Russell

The announcement comes as the Democratic president seeks Republican support for a sweeping overhaul of U.S. immigration laws, and seeks to rally opposition to a tough new immigration law in Arizona that has caused tension in U.S. relations with Mexico, without seeming soft on illegal border crossings.

The troops will provide intelligence, surveillance and reconnaissance support, intelligence analysis, immediate support to counternarcotics enforcement and training capacity until the Customs and Border Patrol agency can recruit and train more border officers and agents, the official said.

The funds will be used to enhance technology at the border and share information and support between law enforcement agencies as they target illegal trafficking in people, drugs, weapons and money.

SPARRING WITH REPUBLICANS

Arizona’s two U.S. senators, John McCain and Jon Kyl, and Governor Jan Brewer, all Republicans, have asked Obama for more federal support to secure the border.

McCain and Kyl introduced a Senate amendment to force Obama to deploy 6,000 National Guard troops to the border.

The administration rejected the request in a letter to Senate Armed Services Committee Chairman Carl Levin.

“It represents an unwarranted interference with the commander-in-chief’s responsibilities,” wrote national security adviser James Jones and counterterrorism chief John Brennan.

Illegal immigration across the border with Mexico has been in intense focus since Arizona last month passed the law to drive 460,000 illegal immigrants out of the desert state, which straddles one of the principal corridors for human and drug smugglers heading up from Mexico.

The law requires state and local police to investigate the immigration status of people they reasonably suspect are in the country illegally.

It was a central issue last week during a state visit to Washington by Mexican President Felipe Calderon, who said the law discriminated against foreign-born workers.

Mexican officials said on Tuesday they respected Obama’s right to make the decision, but thought Washington should address problems originating on its side of the border.

“The Mexican government considers that the decision ... should translate into the channeling of additional resources to make efforts more effective to combat the trafficking of illegal arms and cash to Mexico,” the Mexican foreign ministry said in a statement.

Mexico also urged “shared responsibility” on the fight against drug gangs along the border.

There are currently 344 U.S. National Guard troops working along the border.

U.S. officials are also concerned drug-related violence will cross the border from Mexico, where some 23,000 people have been killed since Calderon took office in late 2006 as drug gangs fight turf wars and battle federal agents and troops.

A prominent cattleman, Robert Krentz, was shot dead on his ranch in southeast Arizona in late March. Police followed tracks from the scene of the shooting to the Mexican border, but made no arrests.

Cochise County sheriff Larry Dever, whose office is investigating Krentz’s death, said he doubted that many troops would make much difference, given the border’s nearly 2,000-mile (3200-km) length.

“If you put 1,200 in perspective ... that’s about one every two miles ... so we’re woefully short of doing anything significant, unless they are all deployed in a very specific area,” he told Reuters.

Obama met on Tuesday with Senate Republicans, none of whom has come out in support of his immigration plan. He pushed them to support an overhaul, which he said he wants passed this year, but did not bring up the National Guard plan.

Kyl said it was not a good idea for Democrats to “try to hold hostage the security of the border in order to get comprehensive immigration reform passed.”