President-elect Barack Obama, far right, announces his national security team during a news conference Monday in Chicago. Standing behind Obama are from left to right, Attorney General-designate Eric Holder, Homeland Security Secretary-designate Janet Napolitano, Secretary of Defense Robert Gates, Vice President-elect Joe Biden, Secretary of State-designate Hillary Rodham Clinton, National Security Adviser-designate Ret. Marine Gen. James Jones and United Nations Ambassador-designate Susan Rice.

Chicago ? Barack Obama promised “a new dawn of American leadership” in a troubled world Monday, announcing a strong-willed national security team headed by Hillary Rodham Clinton, who fought him long and bitterly for the presidency, and Robert Gates, the man who has been running two wars for George W. Bush.

The president-elect said he hadn’t changed his mind about bringing most U.S. combat troops home from Iraq within 16 months but added a cautionary note — he’ll consult with his military commanders first.

While his new team may be a bit more centrist — some war opponents might even say hawkish — than many Obama supporters might prefer, he said the withdrawal timetable he emphasized in the presidential campaign is still “the right time frame.”

Clinton, as secretary of state, and Gates, remaining as defense secretary, will be the most prominent faces — besides Obama’s own — of the new administration’s effort to revamp U.S. policy abroad.

At a Chicago news conference, Obama also tapped top advisers Eric Holder as attorney general and Susan Rice as ambassador to the United Nations. He named Arizona Gov. Janet Napolitano to be homeland security secretary and retired Marine Gen. James Jones as White House national security adviser.

The choices had been telegraphed days earlier but were remarkable all the same — still another major turn in Clinton’s extraordinary career, a show of faith in Gates and action to support Obama’s frequent talk of desiring robust debate among seasoned, opinionated people in his inner circle.

Denouncing White House “group think,” Obama signaled a break from President Bush’s tendency toward an insular management style and go-with-the-gut diplomacy.

“The time has come for a new beginning,” said Obama, flanked by flags on a stage with Vice President-elect Joe Biden and his newest appointees. While Gates will stay at the Pentagon, Obama said the military’s new mission will be “responsibly ending the war in Iraq through a successful transition to Iraqi control.”

He said a newly completed agreement between Iraq and the Bush administration covering U.S. troops signals “a transition period in which our mission is changing.” He added: “It indicates we are now on a glide path to reduce our forces in Iraq.”

Obama has now selected half his Cabinet, including the high-profile jobs at State, Defense, Justice and Treasury. A week ago, he named his economic team, led by Timothy Geithner as treasury secretary. And soon he plans to announce New Mexico Gov. Bill Richardson as commerce secretary and former Senate Majority Leader Tom Daschle as health and human services secretary.

Obama’s picks suggest he is mindful of his own relative inexperience; most of the appointees have decades more experience in government than he does. The selections also reflect his long-voiced desire to invite divergent viewpoints to chart the best course for the country.

“I assembled this team because I’m a strong believer in strong personalities and strong opinions,” he said. “I think that’s how the best decisions are made. … So I’m going to be welcoming a vigorous debate inside the White House.”

“But understand I will be setting policy as president,” he added. He said he will be responsible for “the vision that this team carries out, and I expect them to implement that vision once decisions are made.”

Quoting Harry S. Truman, Obama said: “The buck will stop with me.”