CAMP VICTORY, Iraq — In a change of plans, American commanders in Iraq have decided to keep the bulk of their forces concentrated in Baghdad when the U.S. troop buildup ends next year, removing extra troops instead from outlying areas of the country.

The change represents the military’s first attempt to confront its big challenge in 2008: how to reduce the number of troops without sacrificing security.

The shift in deployment strategy, described by senior U.S. military officials in Iraq and Washington, D.C., is based on concerns that despite recent improvements, the capital could erupt again into widespread violence without an imposing American military presence.

A year ago, when U.S. patrols in Baghdad were sparse and sectarian killings were spiraling out of control, the troop buildup was proposed in part to establish order in the capital. Over the last four months, violence in the capital has begun to abate.

But the most significant improvements have been in outlying areas, where the first surge troops arrived at the start of the year, followed by gradual improvements in Baghdad. Planners at first thought it would be the other way around.

“There was a sense we would focus very significantly on Baghdad and change would come from Baghdad-out,” said a senior military official in Washington, who like others spoke on condition of anonymity when discussing troop strategy. “What we are seeing is just the opposite, it is probably outside-in, toward Baghdad.”

The withdrawals are occurring over the next eight months as the troop surge that President Bush ordered last January gradually comes to an end. Plans call for reducing troops that reached a peak of about 170,000 to pre-buildup levels of about 135,000.

The new planning is not without risk and controversy. The change in U.S. deployment strategy probably will shift the balance of political power in the country by putting much greater authority over provincial affairs in the hands of local and regional officials. That will increase the influence of the local and provincial governments and offset the authority of the Shiite-dominated central government.

In addition, some of the early troop reductions will take place in areas such as Anbar province, the site of raging insurgency in the recent past.

Nonetheless, the international military pullback from outlying areas is under way. On Sunday, the British will hand over authority for Basra and the south to the Iraqi government. Next, U.S. officers expect to hand over western provinces to Iraqi control, including Anbar, followed by still-precarious provinces north of Baghdad, say military leaders in Washington and Iraq.

The new U.S. military view worries officials in the Shiite-dominated central government who fear their power will be diminished. The Shiite officials have expressed concern over U.S. plans to hand over security responsibilities to recently recruited police forces, particularly in Sunni strongholds such as Anbar where the new police forces are mostly Sunni.

But the day-to-day commander in Iraq, Army Lt. Gen. Raymond Odierno, and his staff believe the increasing competence of provincial security and political leaders will put pressure on the government in Baghdad that “will breed a better central government,” said his chief of staff, Brig. Gen. Joseph Anderson.

“There are different schools of thought here,” Anderson said. “Our school of thought is provincial capacity will ultimately lead to enhanced central government capacity. That’s our view.”

So far, military officials have sought to design the troop reduction in a way that avoids creation of security gaps. But by the spring, when the number of U.S. brigades in Iraq is reduced from the current 19 to 17, significant turnovers of security responsibility in outlying provinces are inevitable, Odierno said. Those turnovers should accelerate the shift away from a pure counterinsurgency strategy. Military leaders in Washington have been pressing generals in Baghdad to move toward what they call “tactical overwatch.” Under that strategy, Iraqi troops would take the lead in most operations, and U.S. troops would be called in only when problems occur.