eader Harry Reid and House Speaker Nancy Pelosi urged Bush to begin pulling troops out of Iraq in four to six months. They also asked the president to begin shifting the mission of U.S. forces there from combat to training and logistical support of the Iraqis.

"We are well past the point of more troops for Iraq," Pelosi, D-Calif., and Reid, D-Nev., wrote a day after their party took control of Capitol Hill.

The Democrats' criticism of a troop buildup was not new. But the letter underscored a new reality for Bush: With the new congressional leadership, his Iraq policy will be challenged at every turn by lawmakers.

The president plans to replace his two top generals in Iraq, a defense official, speaking on grounds of anonymity, told The Associated Press. Defense officials said they expected the appointments to be announced later Friday.

NBC News reported that White House sources expect the outgoing Iraq commander, Gen. George Casey, to be nominated to become Army chief of staff later Friday.

Bush next week will unveil his Iraq strategy, which is expected to entail new political, military and economic steps to win the war. The military approach, which has attracted the most attention and skepticism from Congress, is expected to include an increase in U.S. forces, possibly 9,000 additional troops deployed to the Baghdad capital alone.

A New Team for Iraq Policy

"One thing is for certain: I will want to make sure the mission is clear and specific and can be accomplished," Bush said Thursday.

Before the president provides more details, however, he is putting in place a new team to help oversee his Iraq policy.

Ryan Crocker, a veteran American diplomat now U.S. envoy to Pakistan, was expected to replace Zalmay Khalilzad as the U.S. ambassador to Iraq. Khalilzad will be nominated to become the U.S. ambassador to the United Nations, according to a senior Bush administration official.

Gen. John Abizaid, the top U.S. commander in the Middle East, and Casey are both expected to leave their jobs in coming weeks.

The defense official, who insisted on anonymity because formal announcements are still pending, said that Bush wants to replace Abizaid with Adm. William Fallon, the top U.S. commander in the Pacific, and that Casey's replacement would be Army Lt. Gen. David Petraeus, who headed the effort to train Iraqi security forces.

Also, Bush nominated retired Vice Adm. Mike McConnell, a veteran of more than 25 years in intelligence, to succeed John Negroponte as national intelligence director.

Sen. Daniel K. Inouye, D-Hawaii, a member of the Senate Defense appropriations subcommittee, said of Fallon: "He's highly knowledgeable and well-educated and respected. I would think that his nomination, if the president is to submit it, would go flying through."

Each of the personnel changes comes on the heels of Defense Secretary Robert Gates replacing Donald Rumsfeld, the architect of the unpopular war.

Besides ushering in new personnel, Bush on Friday was to discuss his plans for the Iraq war privately with more than a dozen senators, a list that includes some of his biggest critics, as well as his most ardent supporters.

Briefings with lawmakers were expected to continue through next week, culminating in a meeting with bipartisan leadership on Wednesday, according to lawmakers and aides.

One option being considered by Bush includes sending 8,000 to 9,000 more troops to Iraq, primarily to reinforce Baghdad. There are roughly 140,000 troops in Iraq.

The option involves sending two additional Army brigades, or roughly 7,000 soldiers, to Baghdad, and two Marine battalions, totaling about 1,500 troops, to western Anbar Province, the center of the Sunni Arab insurgency.

Bush Looks to Signal Fresh Approach

This concern was echoed by Abizaid in testimony on Capitol Hill in November. He said 20,000 more troops could be deployed, but that the Army and Marine Corps are too taxed to sustain the increase for long.

Giving Fallon and Petraeus the top military posts in the Middle East would help Bush assert that he is taking a fresh approach, and help pave the way for him to turn policy there in a new direction.

As with Abizaid, Casey also has expressed reservations about the potential effectiveness of boosting troop strength in Iraq. He told reporters in Iraq last month that he is "not necessarily opposed to the idea" of sending in more troops, but said any increase would have to "help us progress to our strategic objectives."

Besides military, Bush's new plan is expected to contain economic, political and diplomatic components.

Given the need to reduce high unemployment and draw Iraqis away from Shiite militias and the Sunni insurgency, the president is considering loans to businesses. He is looking at getting Iraqis into short-term jobs by proposing a significant increase in the discretionary funds that military commanders can use for reconstruction projects.

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