WASHINGTON (Reuters) - Republican presidential candidate Fred Thompson on Tuesday urged more defense spending and a much larger military to shore up what he called major weaknesses in national security.

Republican presidential candidate Fred Thompson speaks during a campaign stop in Indianola, Iowa, November 12, 2007. REUTERS/Shannon Stapleton

In a speech at the Citadel military college in the early primary voting state of South Carolina, Thompson planned to call for a significant boost in the size of the Army to 775,000 troops and the Marine Corps to 225,000 members.

He did not describe how he would pay for the increases in the prepared remarks. The Pentagon already is expanding the Army to 547,000 by 2010 from 482,000 and the Marines to 202,000 from 175,000.

“We have major shortcomings in U.S. defense capabilities. To confront these shortcomings, we must address several key priorities,” Thompson said.

“Too many commitments today leave our armed forces capable of meeting too few contingencies tomorrow ... Half-measures and small increases will no longer do.”

The U.S. military has had trouble recruiting in recent years, in part because of the wars in Iraq and Afghanistan. It now offers cash inducements and has relaxed academic requirements for new recruits.

Thompson is running second behind former New York mayor Rudy Giuliani for the Republican presidential nomination in most recent polls but has been widely criticized for running a lackluster campaign so far.

He won a welcome boost on Tuesday, gaining the endorsement of the National Right to Life Committee, a lobbying group that has led the fight against abortion rights. That might boost him in Iowa which on January 3 holds the first binding vote in the state-by-state presidential nomination battles.

In his speech, Thompson also planned to call for boosting defense spending to 4.5 percent of U.S. gross domestic product, excluding the cost of the wars in Iraq and Afghanistan. That would be up from about 4.1 percent of GDP now, which Thompson says includes money for Iraq and Afghanistan.

“We must begin by rebuilding our military with the full recognition that national security comes at a price,” he said.

President George W. Bush on Tuesday signed a $460 billion measure to fund the Pentagon for the 2008 fiscal year that began October 1 and Congress is weighing a separate $196 billion bill to fund the two wars.

(Editing by David Alexander)