WASHINGTON (Reuters) - United States Vice-President Joe Biden says he might run for president in 2016, and one of the factors he will consider in making his decision is whether he has as much energy then as he does now.

Mr Biden, 70, gave his thoughts on the possibility of a race for the Democratic presidential nomination in an interview with Go magazine.

Most Democrats have their eyes on former secretary of state Hillary Clinton, watching to see if she launches a second run for the White House, and Mr Biden's comments reflected a view that he wants to be in the discussion as well.

"I can die a happy man never having been president of the United States of America," Mr Biden told Go. "But it doesn't mean I won't run."

Many political analysts doubt Mr Biden will run if Mrs Clinton enters the race. She has made clear she is pondering a bid for the White House, and most polls have her as the runaway favorite to win the party's nomination should she run. But she was considered the favorite in 2008 and was beaten by current President Barack Obama.

Mr Biden noted that in his office he has two portraits, each of them of vice-presidents who later became president, Thomas Jefferson and John Adams.

"The judgment I'll make is, first of all, am I still as full of as much energy as I have now - do I feel this?" he said.

"Number two, do I think I'm the best person in the position to move the ball? And, you know, we'll see where the hell I am."