“The secretary of state is America’s face to the world, and in Dr Rice, the world will see the strength, the grace and the decency of our country,” Mr Bush said with Ms Rice at his side in the White House.

The president also announced that Ms Rice’s deputy, Stephen Hadley, would replace her as national security adviser, a post which, unlike secretary of state, does not require confirmation by the US Senate.

“Steve is a man of wisdom and good judgment. He has earned my trust. And I look forward to his continued vital service on my national security team,” said Mr Bush during prepared remarks in the Roosevelt Room of the White House.

Listing US diplomatic priorities for his second four-year term, Mr Bush said Ms Rice would prosecute the global war on terrorism, pursue efforts to end the Arab-Israel conflict and help spread democracy across the Middle East.

“During the last four years, I’ve relied on her counsel, benefited from her great experience and appreciated her sound and steady judgment. And now I’m honoured that she has agreed to serve in my cabinet,” he said.

The US President omitted any mention of repairing trans-Atlantic relations frayed by the March 2003 US-led invasion of Iraq, a task he had cited as a top goal just last week when he said the first overseas trip of his new term would be to Europe.

Both the president and Ms Rice paid tribute to Mr Powell, who announced on Monday that he was leaving after submitting his resignation letter on Friday.

Mr Powell was absent from the brief ceremony.

“He has been one of the most effective and admired diplomats in America’s history,” Mr Bush said of Mr Powell.

The former US Secretary of State was frequently on the defensive in the face of more hawkish policymakers on key issues like North Korea and Iraq.

Mr Powell “has helped to rally the world in a global war. He’s helped to revolve dangerous regional conflicts. He has been tireless and selfless and principled, and our entire nation is grateful for his lifetime of service,” said Mr Bush.

“It is humbling to imagine succeeding my dear friend and mentor, Colin Powell,” said Ms Rice. “Colin Powell has been a great and inspirational secretary of state. It was my honour to serve alongside him, and he will be missed.”

If Ms Rice’s nomination is confirmed by the Senate she would become only the second woman to hold the top cabinet post, after Madeleine Albright, Powell’s predecessor.

Meanwhile US State Department number two Richard Armitage has followed his boss and friend Colin Powell in handing in his resignation.

The 59-year-old deputy secretary of state sent a formal letter of resignation as Mr Powell’s departure was being announced, according to State Department spokesman Richard Boucher.