He cited last week's terrorist attack in Mumbai and the wars in Iraq and Afghanistan, asserting that "the national security challenges we face are just as grave and just as urgent as our economic crisis."
During the news conference, Obama also gave hints of his foreign policy priorities. He said he still believed that a 16-month period for withdrawal of U.S. combat troops from Iraq, which he promised in the campaign, is "the right time frame," and that Gates and the military leadership would be ordered from the outset to devise a withdrawal plan.
Obama said he would consider the recommendations of his military advisors on implementing the plan and would take into account the safety of U.S. troops and Iraqi interests.
He also cited his interest in pushing from the beginning for Arab-Israeli peace, even though many observers are now deeply pessimistic about the conflict.
Critics have questioned whether Obama would be able to guide U.S. foreign policy with a team of strong-willed veterans led by Clinton, his fierce rival during the long presidential primary campaign. But Obama said the choice reflected his belief in "strong personalities and strong opinions. I think that's how the best decisions are made."
Clinton, Gates and Jones have worked together and agree on some, though not all, issues. Yet the holders of those three posts have often collided in past administrations, especially under the pressure of wars and other foreign policy crises.
Obama said the team members believe they can get along. He promised: "I will be responsible for the vision that this team carries out."
The president-elect has chosen a centrist team in part to ensure broad support as he takes on the politically risky effort of winding down the Iraq commitment while seeking a new approach to the Afghan war, which he says the U.S. is now losing.
In introducing his team, Obama stressed qualifications that were likely to appeal to conservatives as well as those of other political stripes.
He pointed out that Jones, who served in the Vietnam War, won a Silver Star and that "generations of his family served heroically on the battlefield." He noted that Gates had won respect in both political parties "for his pragmatism and competence."
Obama's selections have won praise from Republicans. Sen. Richard G. Lugar of Indiana, the senior Republican on the foreign relations committee, said on ABC's "This Week" that Obama's choices were "excellent."
