'Missing' US governor was on private Argentina trip

* South Carolina governor says he was on trip to Argentina

* Sanford's aides had said he was hiking on U.S. trail

* Secretive absence seen hurting presidential aspirations

By Matthew Bigg

ATLANTA, June 24 (Reuters) - South Carolina Governor Mark Sanford returned to the United States on Wednesday from a secret private trip to Argentina, ending days of speculation over his whereabouts and raising questions about his judgment.

Sanford is the chairman of the Republican Governors' Association and a prominent fiscal conservative who has been talked about as a potential Republican candidate for the 2012 U.S. presidential election.

Analysts said his mystery retreat to South America could damage his political career if he has presidential aspirations.

When media reported Sanford's whereabouts were unknown since last Thursday and that even his wife did not know where he was, his aides said he was hiking on the Appalachian Trail in the eastern United States to get away for a break after a tough state legislative session.

During his absence, some South Carolina politicians accused him of abdicating responsibility for state affairs by leaving without giving details of where he was going and remaining out of contact.

Sanford flew to Atlanta early on Wednesday and told reporters for The State, South Carolina's biggest newspaper, he had decided at the last minute to go to Argentina and drive along its coastline.

"I wanted to do something exotic ... to get out of the bubble I am in," he told the paper, adding he had traveled alone.

CONCERNS FOR 2012

Sanford gained prominence this year by opposing Democratic President Barack Obama's economic stimulus bill and rejecting $700 million of South Carolina's portion of the funds on grounds that the law was reckless and would undermine the state's fiscal stability.

The state's Supreme Court ruled this month that the federal cash must be accepted.

Interest in Sanford's mystery absence will blow over in the short term but could hurt him if he has his eye on the White House, said Robert Oldendick, professor of political science at the University of South Carolina.

"He has gotten publicity as a true conservative spokesman who was ideologically driven to resist the stimulus money with an eye on the presidency in 2012," said Oldendick.

"If he disappeared ... without telling staff or his family, then that raises a question of 'Is this the type of person we want with the responsibility for being in charge of nuclear weapons or in crisis situations?'"

Last week, Senator John Ensign, another potential Republican presidential contender in 2012, announced he had an affair with a woman who was a close family friend and resigned his position as chairman of the Republican Policy Committee.

The eastern seaboard state of South Carolina has a population of 4 million.

Its production includes chemical and paper products, textiles, tobacco, soybeans and cotton. Military bases and nuclear facilities are important to its economy, while tourism is also a major source of revenue. (Editing by Pascal Fletcher and John O'Callaghan)