Washington ? American combat deaths in Iraq have dropped by half in the three months since the buildup of 28,000 additional U.S. troops reached full strength, surprising analysts and dividing them as to why.

U.S. officials had predicted that the increase would lead to higher American casualties as the troops “took the fight to the enemy.” But that hasn’t happened, even though U.S. forces have launched major offensives involving thousands of troops north and south of Baghdad.

American combat casualties have dropped to their lowest levels this year, even as violence involving Iraqis remains high.

Military officials and observers are wondering whether the lower U.S. casualties are a sign of success or an indication that insurgents and militiamen simply chose a different battlefield when the Americans mounted their offensive in Iraq’s capital.

“Nobody here is doing cartwheels yet,” said one senior military official at the Pentagon, who requested anonymity to speak freely.

One British analyst, using the example of the British drawdown of forces in southern Iraq, suggested that the lower numbers may mean that American troops are irrelevant to the many conflicts racking Iraq: ethnic cleansing of neighborhoods in Baghdad, massive bombings of religious minorities by Sunni Muslim extremists in northern Iraq and Shiite-on-Shiite-Muslim violence in southern Iraq.

Instead, he suggested, Iraq’s armed factions and politicians already are thinking beyond the troop buildup.

“Everyone is preparing for what happens” after U.S. forces leave, said James Denselow, an Iraq specialist at the London-based Chatham House, a foreign affairs research institute.

Supporters of the troop increase say the lower casualty figures show that the larger number of troops and the counterinsurgency approach of Gen. David Petraeus have turned Iraqi citizens against armed groups, putting them on the run and fracturing them.

“The population is progressively turning to coalition and Iraqi forces and making a positive difference in bringing security to their towns, villages and neighborhoods,” Lt. Gen. Raymond Odierno, the No. 2 commander, said last month.

Others, however, noted that as U.S. combat deaths have dropped, deaths among Iraqi civilians have remained constant, and the “ethnic cleansing” – the street-by-street homogenization – of Baghdad’s neighborhoods has continued almost unabated.

While the Shiite Mahdi Army militia has lowered its profile in the capital, it’s battled the rival Badr Organization of the Supreme Islamic Iraqi Council for control of southern Iraq. Two southern provincial governors have been assassinated, many allege by the Mahdi Army. In northern Iraq, suspected Sunni insurgents killed more than 400 people in a coordinated attack on two villages, the largest terrorist act since the 9-11 attacks on New York and Washington.

Most agree that a second reason for the decline is the dramatic change of conditions in Anbar province, where former Sunni insurgents have teamed up with American troops to rid the province of the group al-Qaida in Iraq. About one-third of U.S. casualties have been in Anbar province, but that’s shifted since the troop increase began. In August, about 10 percent of U.S. casualties occurred there, compared with 30 percent in January, when the buildup began.

Shiites are fighting one another for control of the southern provinces. Some Pentagon commanders have told McClatchy Newspapers that they think rebel cleric Muqtada al Sadr’s Mahdi Army left Baghdad before the troop increase began to fight in the south. Throughout the buildup, Sadr has issued statements discouraging his followers from attacking U.S. forces and Baghdad’s fortified Green Zone.