President Bush plans to appoint a new, higher-ranking military commander for Iraq, capping an overhaul of the command structure that is likely to replace Army Lt. Gen. Ricardo S. Sanchez as the top general on the ground there, Pentagon and other administration officials said yesterday.

Sanchez has been besieged lately by questions about his oversight of detainee operations in Iraq, especially his role in the scandal over the abuse of Iraqi detainees by U.S. soldiers at the Abu Ghraib prison outside Baghdad. But administration officials said the move to install a new four-star commander has been under consideration for months, well before the mistreatment of detainees became major news.

It is not clear what will happen to Sanchez. For months senior commanders have said privately that plans envisioned a new role for him, possibly as head of the U.S. Southern Command, which oversees military operations in South America, the Caribbean and most of Central America. But that position requires a congressional confirmation hearing, which would be likely to lead to a new round of questions about the Abu Ghraib scandal and Sanchez's actions in dealing with it.

Sanchez commands most regular Army and Marine units in Iraq. But there are four other U.S. three-star generals in Iraq. The new commander will outrank all those officers and, unlike Sanchez, will also have authority over all U.S. military units there, including Special Operations forces and the Iraq Survey Group, which focuses on searching for weapons of mass destruction.

The leading contender for the new, four-star job has been Gen. George W. Casey Jr., the Army's second-in-command, officials said. The other senior officer under consideration for the post is Army Lt. Gen. Bantz J. Craddock, the senior military assistant to Defense Secretary Donald H. Rumsfeld. But several officials said yesterday that Rumsfeld seemed in the past week to pull back from formally proposing Craddock.

The official word from the Pentagon late yesterday was that no final decision had been taken either to establish the four-star billet or to fill it with someone other than Sanchez. "If we had something like that to announce, we would," said Bryan Whitman, a senior Pentagon spokesman. "Any speculation prior to an announcement would be irresponsible."

At the same time, other officials noted that Sanchez has served in Iraq for just over a year and that Army and Marine Corps division commanders all have rotated out of the country during that time.

Just 10 days ago, the Pentagon formally completed a realignment of the military structure in Iraq intended to allow the top commander in the country to focus on bigger-picture strategic concerns while handing off responsibilities for battling insurgents and developing new Iraqi security services to deputies. While Sanchez now serves as head of this revamped structure, called Multinational Force Iraq, the question of whether the post would become a four-star position had been uncertain for months.

Army Gen. John P. Abizaid, who as head of the U.S. Central Command supervises U.S. military operations in the Persian Gulf region, had been pushing to make the job a four-star billet to give the senior commander added authority. As such, it would be analogous to the top U.S. commander in South Korea, who is not formally a regional commander but is treated as such.

Both the officers being considered for the post are longtime colleagues of Abizaid's.

Four years ago, Craddock succeeded him as commander of the Army's 1st Infantry Division. Casey followed Abizaid in two key Pentagon positions, first as the head of planning for the staff of the Joint Chiefs and then as the staff's director.

Sanchez is considered by many of his peers to be a solid soldier who has been overwhelmed by the task of commanding the U.S. mission in Iraq.

"I do not see in him the kind of dynamic leadership and insightful strategy that is needed to win this war," said Andrew Krepinevich, a retired Army officer who is now executive director of the Center for Strategic and Budgetary Assessments, a defense think tank.

But retired Army Gen. Barry McCaffrey, who commanded Sanchez in the 1991 Gulf War, remembered Sanchez, who led a battalion in McCaffrey's 24th Infantry Division, as one of his best subordinate commanders. "A terrific combat commander, led from the front, great personal courage, soldiers trusted him," McCaffrey said.

Even so, McCaffrey was less than glowing in his assessment of Sanchez's performance in Iraq.

"I think Rick got sucked into Bremer's CPA and rarely broke out of his orbit," McCaffrey said, referring to the Coalition Provisional Authority, headed by civilian administrator L. Paul Bremer.

Gen. George W. Casey Jr., left, and Lt. Gen. Bantz J. Craddock are considered leading contenders for a new four-star post as top commander in Iraq.