Obama to make immigration case at Mexico border

* Hispanics major voting bloc in 2012 presidential vote

* Obama keeping National Guard at border, adding agents

* Sensitive issue energizes GOP, worries businesses

By Patricia Zengerle

WASHINGTON, May 10 (Reuters) - President Barack Obama will make his case for immigration reform on Tuesday on a visit to the U.S. border with Mexico, reaching out to Hispanic voters whose support he is counting on to win re-election next year.

Top aides said Obama would contend in a speech in El Paso, Texas, that tightening border controls while providing a path to citizenship for some illegal immigrants will improve U.S. security as well as the economy.

"Comprehensive immigration reform would be a plus, not a drag, on the federal budget," a senior administration official told reporters, requesting anonymity as he spoke before the president's speech.

The official said the cost of such overhaul would be $54 billion, but the revenue increase would be $66 billion, adding: "Bringing people to a path where they can be taxpayers is obviously going to be more of a plus than allowing the status quo to continue."

The White House will also seek to extend the stay of 1,200 National Guard troops posted at the border who are due to leave in June, another official said, though the administration is still determining how to pay for them.

There are an estimated 11 million illegal immigrants living in the United States, many of them Latin Americans who crossed the porous 2,000 mile (3,220 km) frontier with Mexico.

Obama has pledged repeatedly to fix the U.S. immigration system to address citizenship concerns and make it easier for businesses to plan, but the issue has taken a back seat to other matters such as economic recovery and healthcare reform.

In December the "Dream Act," which would have given a path to citizenship for illegal immigrants brought to the United States as children, failed to pass -- a disappointment for many Hispanic Americans.

Immigration is a politically explosive issue in the United States and Obama is not expected to be able to push through a broad overhaul before the November 2012 presidential vote.

In Texas, Obama is expected to stress the point that leading Republicans -- including former President George W. Bush -- have backed immigration reform in the past, and call for bipartisan action.

He will need to convince Hispanics something will happen on the issue if he wins a second term, said Audrey Singer, an immigration expert at the Brookings Institution.

"If this group who has been promised over Obama's presidency, but also Bush's, that things were going to change, if they keep getting disappointed, it's hard to say what that is going to mean," Singer said.

RALLYING CRY

Tightening immigration laws -- and opposing the idea of giving "amnesty" to those who broke the law sneaking into the country -- has become a rallying cry for many Republicans who want a clampdown to keep drug crime from crossing the border.

"The president can pander all he wants to, make as many speeches as he wants to," said Lamar Smith, a Texas Republican who chairs the main committee in the U.S. House of Representatives that would consider immigration legislation.

"I do not see amnesty (for illegal immigrants) coming up before the ... committee that I chair."

In August Obama signed a $600 million bill to tighten security along the Mexican border, including the hiring of 1,500 border patrol agents, customs inspectors and law enforcement officials.

The National Guard troops were sent to fill the gap while those new agents were trained.

Obama's failure to get broader legislation on immigration through Congress has upset many Hispanic voters, especially because the United States deported nearly 400,000 illegal immigrants last year.

The 50.5 million Hispanics in the United States represent 16 percent of the population and are the fastest-growing U.S. minority group. They voted for Obama by a margin of more than two-to-one in 2008, according to the Pew Hispanic Center.

Immigration is a concern for local politicians in southern U.S. states and many business owners who struggle with the cost of immigration and uncertainty about how laws may change.

"There's a lot of pressure percolating up from all different camps," Singer said.

Obama and other Washington officials have consulted with business executives, Hispanic celebrities, local politicians and labor and religious leaders on immigration system reform.

The administration will also announce on Tuesday plans for dozens of "community conversations" on the issue around the country. (Additional reporting by Jim Forsyth and Tim Gaynor; Editing by Laura MacInnis)