Of Brennan, Obama said he had an "invaluable perspective" on global affairs. He has traveled extensively in the Middle East and was once CIA station chief in Saudi Arabia.
Sen. John McCain, R-Ariz., issued a statement shortly after the White House announcement on Brennan, saying he had "many questions and concerns about his nomination to be director of the Central Intelligence Agency, especially what role he played in the so-called enhanced interrogation programs while serving at the CIA during the last administration, as well as his public defense of those programs."
Hagel, something of a maverick among Republican senators during his two terms, has criticized the discussion of a military strike by either the U.S. or Israel against Iran. He also irritated some Israel backers with his reference to the "Jewish lobby" in the United States. And he has backed efforts to bring Iran to the table for future peace talks in Afghanistan.
Obama said that when he and Hagel served in the Senate "I came to admire his courage and his judgment, his willingness to speak his mind even if it wasn't popular, even if it defied the conventional wisdom. That's exactly the spirit I want on my national security team - a recognition that when it comes to the defense of our country, we are not Democrats or Republicans. We are Americans."
Sen. Lindsay Graham, R-S.C., has called Hagel's foreign policy views "outside the mainstream" and has said he would be "the most antagonistic secretary of defense toward the state of Israel in our nation's history."
Although bracing for a confirmation fight over Hagel, the administration has expressed confidence both its nominees will be confirmed.
Supporters of Hagel's nomination have said it would be hard for Republicans to reject a former colleague, especially one who's a Vietnam veteran and served on the Foreign Relations and Intelligence committees.
White House spokesman Jay Carney defended both of Obama selections.
Carney said Hagel's "record demonstrates that he is in sync with the president's policies." He said Obama had worked closely with Hagel both as a senator and with Hagel as co-chairman of his White House intelligence advisory board.
Despite criticism, he said, "Sen. Hagel's record will convince the Senate to confirm him." If confirmed, Hagel would be the first enlisted Vietnam War veteran to serve in the top Pentagon post.
As to questions about Brennan's connection to harsh interrogation techniques used in the previous administration, Carney said, "It is this president who banned torture as one of his first acts in office" and Brennan was on the same page.