Vice President Joseph R. Biden Jr. said in an interview broadcast on Friday that he would run for president “if no one else” can fight for the domestic, economic and foreign policy issues he cares about and said he would decide by mid-2015.

Mr. Biden did not shy away from signaling his interest in a third run for the White House but his formulation seemed a nod to the looming candidacy of former Secretary of State Hillary Rodham Clinton, who leads him 6 to 1 in a theoretical Democratic nomination contest, according to a recent poll.

“For me,” he told CNN’s Kate Bolduan, “the decision to run or not run is going to be determined by me as to whether I am the best qualified person to focus on the two things I’ve spent my whole life on – giving ordinary people a fighting chance to make it and a sound foreign policy that’s based on rational interests of the United States.”

While he did not mention Mrs. Clinton, he seemed to acknowledge her lead according to a recent Washington Post-ABC News poll. “Doesn’t mean I’m the only guy who can do it,” he said, “but if no one else, I think, can and I think I can, then I’d run. If I don’t, I won’t.”

Asked for a time frame for a decision, he said, “Probably, realistically, a year this summer.”

Mr. Biden, who spent 36 years in the Senate representing Delaware, has run for president twice before, first in 1988 when he dropped out after plagiarism allegations and again in 2008 when he was swamped by both Mrs. Clinton and Barack Obama. After Mr. Obama beat Mrs. Clinton for the nomination, he asked Mr. Biden to join his ticket.

A third run would test Mr. Biden, who has never won a primary or caucus and would be 74 by the time the next president is inaugurated and 82 at the end of a second term. But he is vigorous and in apparent good health. He projects energy and optimism and has been at the center of some of the most important issues in the Obama administration, including managing the withdrawal from Iraq and overseeing the economic stimulus program.

Lately, after last year’s failed fight for gun control legislation, he has been less visible, but he is still handling Iraq for the president as allies of Al Qaeda make a comeback in the western part of the country. He has also been the point person in managing the political crisis in Ukraine and was just assigned by Mr. Obama to conduct a review of job training programs.

Still, Priorities USA Action, the so-called super PAC fund–raising vehicle that backed Mr. Obama in his 2012 re-election campaign, threw its support to Mrs. Clinton last month, indicating that it would raise money for her to fend off possible competitors in 2016.

Mr. Biden gave no appearance of being daunted. “There may be reasons I don’t run,” he said, “but there’s no obvious reason for me why I think I should not run.”