Powell, speaking on NBC's Meet the Press acknowledged Obama's limited experience on the national stage but said the Illinois Democrat had grown over the past two years and displayed the temperament, judgment and intellect to be president and commander in chief.

Powell, a Republican who was President Bush's first secretary of State, said both Obama and McCain would be good presidents and noted that he had been a close friend of McCain's for 25 years.

"It isn't easy for me to disappoint Sen. McCain in the way that I have this morning, and I regret that," Powell said. "But I firmly believe that at this point in America's history, we need a president that will not just continue, even with a new face and with the changes and with some maverick aspects, who will not just continue basically the policies that we have been following in recent years.

"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."

Obama, who called Powell Sunday to thank him for the endorsement, described Powell at a rally in Fayetteville, N.C., as a "great soldier, a great statesman and a great American."

"I have been honored to have the benefit of his wisdom and counsel from time to time over the last few years, but today, I am beyond honored. I am deeply humbled to have the support of Gen. Colin Powell," Obama told a cheering crowd.

McCain, speaking onFox News Sunday, said he disagreed with Powell's decision and noted that he has been endorsed by four other former secretaries of State, all veterans of Republican administrations: Henry Kissinger, James Baker, Lawrence Eagleburger and Alexander Haig.

"Well, I've always admired and respected Gen. Powell. We're longtime friends. This doesn't come as a surprise," McCain said.

Asked whether Powell's endorsement would undercut his campaign's assertion that Obama is not ready to lead, McCain said, "Well, … we have a respectful disagreement, and I think the American people will pay close attention to our message for the future and keeping America secure."

Former House speaker Newt Gingrich, a Republican, said Powell's endorsement would strengthen Obama's contention that he is ready to become commander in chief.

"What that just did in one sound bite — and I assume that sound bite will end up in an ad — is it eliminated the experience factor," Gingrich said on ABC's This Week. "How are you going to say the former chairman of the Joint Chiefs, the former national security adviser, former secretary of State was taken in?"

I'm glad General Powell is endorsing Barack Obama.  He knows that our economy is in bad shape.  He isn't the only Republican out here that's sided with the Obama Campaign.  With John McCain leading our country, things will continue to go from bad to worse. The rich will continue to get richer and the poor, poorer. One of my co-workers said it best. "If you weren't effect by the way the country has been run the past 8 years, then you should have no problem voting for McCain."