President Bush yesterday nominated Army Gen. George W. Casey Jr. to take over as the highest-ranking military commander in Iraq, which would make Casey the first four-star general stationed there since the U.S.-led invasion.

Casey -- whose appointment must be confirmed by the Senate -- would take the place of Army Lt. Gen. Ricardo S. Sanchez amid an overhaul of the command structure there and questions about Sanchez's oversight of the military's treatment of prisoners.

Last week, Sanchez removed himself as overseer of an investigation into abuses at the Abu Ghraib prison and asked that a higher-ranking officer take responsibility for the probe. That cleared the way for investigators to question Sanchez, who has said he did not sanction maltreatment and did not know about abuse of Abu Ghraib prisoners until January, when a soldier turned in photographs showing it.

The decision to place a four-star general in Iraq as the head of multinational forces means that a single commander will have clear-cut authority over 160,000 U.S. and allied troops who will stay on in Iraq to provide security and confront an insurgency even after an interim Iraqi government assumes authority June 30. Unlike Sanchez, who works alongside four other three-star generals, Casey would outrank all officers and command all U.S. military units there.

Army Gen. John P. Abizaid, who heads the U.S. Central Command and supervises operations in the Persian Gulf region, has been pushing for appointment of a four-star general.

Casey, the Army's second-ranking officer as the vice chief of staff, has commanded the Army's 1st Armored Division and was the chief of staff of the V Corps in Europe in the aftermath of the conflict in Bosnia.

Several who have worked with Casey said they considered him particularly well suited for the position because of that experience in Bosnia, where he displayed a knack for merging diplomatic and military leadership after fighting ended.

"There is not a better choice for this job," said Robert S. Gelbard, former U.S. ambassador to Indonesia and Bolivia who was President Bill Clinton's special envoy to the Balkans and worked with Casey. Gelbard said Casey works well with the State Department and other governments, with a calm temperament and steady hand.

Retired Army Gen. John H. Tilelli Jr., who commanded the 1st Cavalry Division in the Gulf War, said Casey -- who was his chief of staff from 1991 to 1993 -- "has a very good touch."

"He is a quality soldier, a caring leader, an intellect who understands both the political and military issues of situations," Tilelli said. "He can take very complex tasks and break them down."