By Will Dunham

WASHINGTON, Sept 14 (Reuters) - Bernie Sanders, one of the Senate's leading liberals, said on Sunday he is thinking about running for U.S. president in 2016 as either a Democrat or an independent in a move that could complicate Hillary Clinton's path to the White House.

Sanders, an independent from Vermont, could pose a challenge from the left to Clinton, widely seen as the front-runner for the Democratic presidential nomination. She has not officially said she is a candidate but has acted very much like one.

"I think anybody who speaks to the needs of the working class and the middle class of this country and shows the courage to take on the billionaire class, I think that candidate will do pretty well," Sanders told the NBC program "Meet the Press," giving a possible preview of his message in the 2016 campaign.

Sanders is serving his second six-year term in the Senate. He has cultivated a following among some American liberals, especially on economic issues like the growing income disparity between rich and poor and corporate greed. He is a self-described socialist who caucuses with Democrats in the Senate.

"I am thinking about running for president," Sanders said, adding that he must decide whether to run as an independent or wade into the fight for the Democratic nomination.

Sanders is testing the waters in Iowa, a state that holds an important early contest in the nomination process.

"One of the reasons I'm going to Iowa is to get a sense of how people feel about it," he said of his candidacy. "Look, the truth is (there is) profound anger at both political parties, more and more people are becoming independent. The negative is: how do you set up a 50-state infrastructure as an independent?"

Sanders said he has "a lot of respect" for Clinton, but said, "The issue is not Hillary."

With Clinton mindful of the need to appeal to moderates in any general election battle against a Republican in 2016, a Sanders candidacy could force her to the left in the Democratic primaries to head off his challenge.

Conversely, if he runs in the general election as an independent, he could siphon away from her votes from liberals that she could need to beat any Republican nominee.

American liberals have expressed disappointment with President Barack Obama on a range of issues, most recently on his decision to postpone any executive action on immigration even as Republican leaders in the House of Representatives block action on a bipartisan Senate-passed plan.

Sanders said that he has "a lot of disagreements" with Obama, adding: "I think he has not tapped the anger and the frustration that the American people feel on many, many issues." (Reporting by Will Dunham; Editing by Caren Bohan)