WASHINGTON, Aug. 24 — The number of detainees held by the American-led military coalition in Iraq has swelled by 50 percent under the troop increase ordered by President Bush, with the inmate population growing from 16,000 in February to 24,500 today, according to American military officers in Iraq.

Nearly 85 percent of the detainees in custody are Sunni Arabs, the minority faction in Iraq that ruled the country under the government of Saddam Hussein, with the other detainees being Shiite Muslims, the officers say.

Of the Sunni detainees, about 1,800 claim allegiance to a group that calls itself Al Qaeda in Mesopotamia, military officers said. Another 6,000 identify themselves as takfiris, meaning Muslims who believe some other Muslims are not true believers. Such extremists view Shiite Muslims as heretics.

Those statistics would seem to indicate that the main inspiration of the hard-core Sunni insurgency is no longer a desire to restore the old order — a movement that drew from former Baath party members and security officials who served under Mr. Hussein — and has become religious and ideological.