(Reuters) - Most Americans have a favorable view of former U.S. Secretary of State Hillary Clinton and think she will win the 2016 presidential election, according to a Reuters/Ipsos poll released on Thursday.

Fifty-seven percent of Americans who were aware of Clinton hold a favorable opinion of her, compared to 43 percent who see her negatively, according to the online survey. Nearly one-quarter of Republicans said they had a favorable view of Clinton, a Democrat.

While Clinton has not yet declared her candidacy for the White House, she is widely viewed as the front-runner if she does run. Over half of respondents said Clinton would "most likely win" the general election, and over half of Democrats and independents polled said they would vote for her in the party's primary elections, compared to just 10 percent for Vice President Joe Biden.

"Benghazi" was the term that stood out most when respondents who said they had an unfavorable view of Clinton were asked to explain this perspective.

Overall, the term that resonated most among Americans was "strong."

Clinton's foreign policy record has come under fire in recent weeks with the formation of a House of Representatives committee to investigate the 2012 attacks in Benghazi, Libya, that killed the U.S. ambassador and three other Americans.

Clinton on Wednesday defended her tenure at the State Department, where she was the country's top diplomat for four years under President Barack Obama. Her husband, former President Bill Clinton, also played down questions on the health of the former First Lady, who is 66 years old.

While her poll numbers are high, politicians' favorability ratings tend to drop once they declare their candidacy for office and this will likely happen to Clinton too if she chooses to run, Ipsos pollster Chris Jackson said.

"When she's not in public office, you see her favorability shoot up because people who do think good things about her - but don't want to say that when she's a threat to win office - are more likely to talk nicely about her than when she is running for office," he said.

Clinton says she will not decide on a presidential run before November's mid-term elections. She is regarded by 56 percent of Americans as an effective leader, and 62 percent said she knows how to connect with voters.

After over 20 years in the public eye, Clinton also enjoys extremely high levels of name recognition: 96 percent of all respondents said they were aware of her.

"That's presidential level-high," Jackson said. "The only people who have numbers like that are the president, maybe the vice president, and movie stars."

Ipsos polled 1,518 American adults online from May 11 to 15. The poll had a credibility interval - a measure of precision - of 2.9 percentage points.

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