WASHINGTON (Reuters) - Outgoing U.S. Secretary of State Hillary Clinton, who came tantalizingly close to winning the Democratic presidential nomination four years ago, played down the notion she would run again for the White House in 2016 in comments aired on Wednesday.

Clinton for the past four years has served as chief diplomat for President Barack Obama, who edged her for the party's nomination in 2008, but she is stepping down from the post. Obama was elected last month to a second four-year term as president.

Asked during an interview with ABC's Barbara Walters whether she would run for president in 2016, Clinton said: "I've said I really don't believe that that's something I will do again. I am so grateful I had the experience of doing it before."

Clinton, one of the most popular members of Obama's Cabinet and often mentioned as a potential Democratic White House hopeful in 2016, has said she will step down as secretary of state in January.

"It sounds so simple, but I've been, as you know, at the highest levels of American and now international activities for 20 years, and I just thought it was time to take a step off ... maybe do some reading and writing and speaking and teaching," Clinton told ABC.

Clinton, whose husband, Bill Clinton, was president from 1993 to 2001, was elected to the U.S. Senate from New York after her time as first lady. She mounted a vigorous effort in 2008 to become the first woman to claim either the Democratic or Republican U.S. presidential nomination, but was defeated by Obama, who became the first black president.

In the ABC interview, the 65-year-old Clinton said her age would not be a worry if she did opt to run.

"I am, thankfully, knock on wood, not only healthy, but have incredible stamina and energy," she said in excerpts of the interview published on the ABC News website. "I just want to see what else is out there. I've been doing ... this incredibly important and ... satisfying work here in Washington, as I say, for 20 years. I want to get out and spend some time looking at what else I can do to contribute."

She said in the interview that she may work in philanthropy or academia after leaving her post at the State Department.

(Reporting by Will Dunham; Editing by Peter Cooney)