Reich, who served as Labor secretary under Bill Clinton, said in a blog post that "although Hillary Clinton has offered solid and sensible policy proposals, Obama's strike me as even more so."
Reich also said Obama's plans for reforming Social Security and health care have a better chance of succeeding, and his approach to the nation's housing crisis and financial market failures are sounder than the New York senator's.
Reich is a longtime friend of Bill and Hillary Clinton. He ran for governor in Massachusetts in 2002 and now is a professor at the University of California-Berkeley.
A number of other former Clinton cabinet members have endorsed Obama. New Mexico Gov. Bill Richardson, who was U.N. ambassador and energy secretary under Clinton, endorsed former rival Obama in March despite heavy wooing by the former president. Former Denver Mayor Federico Pena, who headed the transportation and energy departments under Clinton, became a co-chair of Obama's campaign last September. Former Clinton Commerce secretaries Norman Mineta and William Daley also have endorsed Obama.
Nunn and Boren will serve as advisers to Obama's National Security Foreign Policy Team.
Nunn served as chairman of the Senate Armed Services Committee from 1987-95, while Boren was the longest-serving chairman of the Senate Select Committee on Intelligence.
Both fall into the moderate-conservative end of the Democratic party's ideological spectrum and gave Bill Clinton trouble during his presidency, trying to tug him to the right on issues while most congressional Democrats were leaning to the left.
Nunn, who recently flirted with his own possible White House bid, said Obama has "a rare ability to restore America's credibility and moral authority and to get others to join us in tackling serious global problems."
Boren, who recently played host to a forum on electoral alternatives, including third-party runs, said: "Our most urgent task is to end the divisions in our country, to stop the political bickering, and to unite our talents and efforts. Americans of all persuasions are pleading with our political leaders to bring us together. I believe Senator Obama is sincerely committed to that effort."
