Even with the reported rise in foreign fighters, several senior officers said, the number estimated to be coming into the country each month is still relatively small -- in the neighborhood of several score. In numerical terms, they said, the insurgency remains essentially homegrown. Iraqi members of extremist Islamic factions, such as the Ansar al Sunna Army, continue to account for many insurgent attacks.
But in terms of overall effect, the foreign fighters who serve as suicide bombers and cause high casualties are having a disproportionate impact, the officers said. The most prominent foreign fighter -- Jordanian-born Abu Musab Zarqawi -- has become Iraq's best-known insurgent, leading a network that has asserted responsibility for some of the bloodier attacks.
Like Zarqawi, a number of foreign fighters are said to be forming tactical partnerships with Iraqi extremist groups to carry out attacks. Though foreigners may drive the suicide cars, Iraqis are frequently behind the scenes operating the networks that provide safe houses, assemble the explosives and arrange other support.
The number of car bombings jumped from 64 in February to 135 in April, according to U.S. military statistics. The proportion of such attacks involving a suicide driver also soared, from about 25 percent to just over 50 percent.
"The car bomb has become the weapon of choice for these guys, it's their precision weapon," another general here said.
Overall, the rate of attacks has climbed from about 30 to 40 a day in February and March to an average of about 70 a day now, by the U.S. military's count.
The main infiltration route into Iraq for foreign fighters continues to be through Syria, the officers here said. Citing terrorist Web sites that advertise for recruits in such countries as Sudan, Libya and Saudi Arabia, the officers said the fighters tended to be flown to Damascus, the Syrian capital, where they were met by facilitators and moved across the border into Iraq.
The spate of car bombings has prompted U.S. commanders to put renewed emphasis on interdicting infiltrators near the border and uncovering bomb-making networks inside Iraq. But commanders are still debating how much to refocus U.S. military operations on the more radical elements of the insurgency.
"Do you focus the preponderance of effort on the former regime elements, or do you shift the targeting effort to another part of the insurgency? That's what people are grappling with right now," said DeFreitas, the intelligence officer.
With the recent rise in attacks, U.S. commanders acknowledge that some of the momentum gained from January's election has been lost. But they say they still hope to make enough progress containing the insurgency and building up Iraqi security forces this year to allow for a significant reduction in U.S. troops early next year. A formal assessment of the progress toward that end is scheduled for next month.
