By Tim Gaynor

PHOENIX (Reuters) - A tough-on-immigration Arizona sheriff, who resigned as co-chair of Mitt Romney's state campaign after allegations he threatened a male lover with deportation, has been cleared of criminal wrongdoing, the state attorney general's office said on Friday.

Earlier this year, Pinal County Sheriff Paul Babeu asked the office to investigate claims made by his former boyfriend, Jose Orozco, accusing the lawman of abuse of authority, threats, and intimidation.

Babeu acknowledged at the time that he is gay and had a personal relationship with Orozco, who was reported to be from Mexico, but denied that he had made any threat to deport him.

The sheriff struck back at Orozco, accusing him in turn of theft of property and identity theft stemming from his former lover's handling of websites and Twitter accounts relating to him.

"The Attorney General's Office will not file charges against either Babeu or Orozco," Solicitor General Dave Cole said in a statement released on Friday.

"The investigation determined that Babeu did not commit any criminal violations and further concluded that, although Orozco conducted himself in a manner that may constitute a violation of the law, there was no reasonable likelihood of conviction on anything more than a misdemeanor charge."

Arizona Attorney General Tom Horne said in February that his office was opening a probe into Babeu's conduct. At the time of the disclosures, Babeu was co-chair of Republican presidential nominee Romney's campaign in Arizona, but promptly stepped down.

Arizona has been in the national spotlight after a U.S. Supreme Court ruling in June allowed a controversial "show-your-papers" measure that requires police to check the status of people they stop and suspect are in the country illegally.

The measure is part of a crackdown on illegal immigration signed in 2010 by Republican Governor Jan Brewer that backers said was needed because of the failure of the federal government to secure the porous border with Mexico. Opponents have slammed the law as a mandate for racial profiling.

Babeu is a strong critic of the stance of President Barack Obama's administration on immigration. Two years ago he appeared in a campaign ad for Republican U.S. Senator John McCain that called for tighter border security and urged the government to "complete the danged fence" on the border with Mexico.

The television spot, which showed McCain and Babeu walking a stretch of the boundary fence in Nogales, raised some eyebrows in Arizona as Pinal County does not border Mexico.

Babeu hoped to ride out the furor and become a Republican congressional candidate this year. But in May he announced he was dropping the bid and would instead run for a second term as sheriff.

(Editing by Cynthia Johnston and Eric Walsh)