Colin Powell, a Republican who was US President Bush's first secretary of state, endorsed Democrat Barack Obama for president Sunday and criticized the tone of Republican John McCain's campaign.

Former Secretary of State Colin Powell speaks during a taping of "Meet the Press" at NBC in Washington October 19, 2008. [Xinhua/Reuters]

The former chairman of the Joint Chiefs of Staff said either candidate, both of them senators, is qualified to be commander in chief. But he said Obama is better suited to handle the nation's economic problems as well as help improve its standing in the world.

"It isn't easy for me to disappoint Sen. McCain in the way that I have this morning, and I regret that," Powell, interviewed on NBC's "Meet the Press," said of his longtime friend, the Arizona senator.

But, he added: "I think we need a transformational figure. I think we need a president who is a generational change and that's why I'm supporting Barack Obama, not out of any lack of respect or admiration for Sen. John McCain."

Powell's endorsement has been much anticipated because he is a Republican with impressive foreign policy credentials, a subject on which Obama, a first-term senator from Illinois, is weak. Powell is a Republican centrist who is popular among moderate voters.

At the same time, Powell is a black man and Obama would be the nation's first black president. Powell said he was cognizant of the racial aspect of his endorsement, but said that was not the dominant factor in his decision. If it was, he said, he would have made the endorsement months ago.

Powell expressed disappointment in the negative tone of McCain's campaign, his choice of Alaska Gov. Sarah Palin as a running mate and McCain's and Palin's decision to focus in the closing weeks of the contest on Obama's ties to 1960s-era radical William Ayers.

A co-founder of the Weather Underground, which claimed responsibility for nonfatal bombings during the Vietnam War-era, Ayers is now a college professor who lives in Obama's Chicago neighborhood. He and Obama also served together on civic boards in Chicago.

"This Bill Ayers situation that's been going on for weeks became something of a central point of the campaign," Powell said. "But Mr. McCain says that he's a washed-out terrorist. Well, then, why do we keep talking about him?"