Secretary of State Condoleezza Rice announced Monday that President Bush will nominate Zalmay Khalilzad to be the U.S. envoy to the United Nations and Ryan Crocker will replace him as U.S. ambassador to Iraq.

Both changes were revealed in news reports last week. The White House on Monday also issued a written statement of the president's intent.

Rice said she has trust and confidence in both men, who will have a lot of work since much remains to be done at the United Nations and in the Middle East.

“Zal has performed heroically and at great personal risk to help Iraqi reformers and responsible leaders build a foundation of democracy in their country,” Rice said in an afternoon statement to reporters. “Ryan will be a demanding boss in our embassy, you can be sure of that, but a fair and inspiring one."

Khalilzad, who is Afghan born, has also served as ambassador to Afghanistan. He will replace John Bolton, who could not win Senate confirmation and resigned last month as his temporary appointment as U.N. ambassador was about to expire.

Bolton said he hopes the Senate moves quickly to confirm Khalilzad.

“Zal has clear ideas and expresses them forcefully,” Bolton told FOX News in his first interview since leaving the world body.

“The past year has shown how clearly important the U.N. is for America and the world, and how important American leadership is to the U.N.,” Rice said at the State Department.

Crocker, a veteran American diplomat who is now U.S. envoy to Pakistan, will replace Khalilzad in Baghdad. He previously served as the director of governance for the Coalition Provisional Authority that moved into Iraq after the fall of Saddam Hussein.

Bush is shuffling his teams of military and diplomatic advisers as he plans to announce a new Iraq strategy on Wednesday.

Gen. John Abizaid, the top U.S. commander overseeing the theater that includes Iraq, will be succeeded by Adm. William Fallon, now Abizaid's counterpart in the Pacific. Army Lt. Gen. David Petraeus is the president's choice to be the new chief commander in Iraq, replacing Gen. George Casey.

Casey in turn will replace the retiring Gen. Peter Schoomaker as Army chief of staff.

Bush has also decided to shift John Negroponte, the national intelligence director, to the State Department to become No. 2 to Rice. Replacing Negroponte would be retired Vice Adm. Mike McConnell, a veteran of more than 25 years in intelligence.'s Melissa Drosjack and The Associated Press contributed to this report.