Powell was the most senior of four members of President George W. Bush's cabinet to quit on Monday.

Bush, who won reelection this month, accepted the resignation of the former top general who directed the 1991 war against Iraq but was only a lukewarm supporter of last year's invasion to oust Saddam Hussein.

Two senior administration officials said the president would name his national security adviser, Rice, to replace Powell. They said the announcement would come on Tuesday.

Bush plans to turn to deputy national security adviser Stephen Hadley to replace Rice, who is one of the president's closest advisers and confidants, said the officials, who spoke on condition of anonymity.

Rice, who was 50 on Sunday, has been tipped for months as a leading contender to succeed Powell. She is a fluent Russian speaker and an expert on arms control.

Hadley, who advised Bush on foreign policy during the 2000 election campaign and took office in January 2001, was also the favorite to take over as national security adviser.

Powell indicated that he has been in longstanding discussions with the president about leaving.

"As we have discussed in recent months, I believe that now that the election is over, the time has come for me to step down as Secretary of State and return to private life," Powell, 67, said in a letter to Bush.

Deputy Secretary of State Richard Armitage, 59, was also likely to step down, officials said.

The White House also announced the departure of Agriculture Secretary Ann Veneman, Energy Secretary Spencer Abraham and Education Secretary Rod Paige. Attorney General John Ashcroft and Commerce Secretary Don Evans quit last week.

But Powell has created the greatest stir, depriving the administration of a highly regarded voice on the international scene at a time when Bush hoped to mend fences after the Iraq war and revive Middle East peace talks.

Bush described Powell as "a soldier, a diplomat, a civic leader, a statesman and a great patriot," and praised his work over the past four years.

Powell "is one of the great public servants of our time," Bush said in a statement.

International tributes

Tributes also flowed in from around the world.

German Foreign Minister Joschka Fischer considered Powell a close friend as well as a colleague. Speaking to reporters following Powell's resignation, Fischer said the Secretary was a man who understood Germany very well, from his time here as a soldier. Despite policy differences between the two countries, Fischer said he never found it difficult to communicate with his counterpart.

"I want to thank him," said German Foreign Minister Joschka Fischer. "We worked very closely together and even in the most critical issues, always as friends ... I wish him all the best in the future."

UN Secretary General Kofi Annan had a "very warm working relationship" with Powell and especially appreciated "support for the United Nations and for multilateral approaches to problem-solving," said Annan spokesman Fred Eckhard.

British Prime Minister Tony Blair called Powell "a remarkable man who has been a good friend to this country over a very long period." German Foreign Minister Joschka Fischer also praised his country's cooperation with Powell.

Japanese government spokesman Hiroyuki Hosodan expressed disappointment but said Powell's resignation would not affect the strong alliance between the United States and Japan.

"As an extremely well-balanced secretary of state, he did a great job," he said of Powell.

Australian Foreign Minister Alexander Downer said Powell had been a great friend to Australia who helped fight terrorism in Asia.

"We will certainly miss him," he said.

Powell is the son of Jamaican immigrants who rose to become a four star general and then the highest ranking African American to serve in the US government. As Rice is also a black the changeover will again be a first in US administration history.

Timing unexpected

The timing of the resignation announcement was unexpected, as Powell plans to visit the Middle East after the death of Palestinian patriarch Yasser Arafat.

The Palestinians' foreign minister, Nabil Shaath, said Powell would visit next week. The State Department said no date had been set.

Powell, scheduled to attend an Asian economic summit in Chile this week, a conference on Iraq in Egypt next week and perhaps a spate of European meetings in December, denied his resignation would affect his work.

"I expect to act fully as secretary of state until I do leave. I will be working hard until the very, very end," he told reporters.

As head of the Joint Chiefs of Staff, Powell was the military architect of the 1991 Gulf War effort to force Iraqi forces out of Kuwait. He saw a turbulent four years as secretary of state marked by the Sept. 11, 2001 attacks and the Iraq invasion.

Internal clashes

Pursuing a pragmatic policy of multilateral diplomacy, Powell reportedly clashed frequently with administration hardliners such as Vice President Dick Cheney and Defense Secretary Donald Rumsfeld who favored pre-emptive military action.

But he refused to talk publicly about the tensions or his future intentions.

Many reports said Powell had felt personally wounded after giving a presentation to the UN Security Council on Feb. 5, 2003 on the US case for an invasion of Iraq because of weapons of mass destruction.

No chemical, biological or nuclear weapons programs have been found.