Waashington ? The Pentagon wants to pull increasing numbers of American troops out of the line of fire in Iraq, but three years after the invasion this latest evolution in the U.S. military’s mission will depend largely on whether Iraqi security forces can handle it.

Whether there will be the first sustained decline in American casualties since the insurgency took hold in late summer 2003 depends on how quickly and fully U.S. troops’ roles are changed. So far more than 2,300 American troops have died in the campaign, with more than 17,000 wounded.

Though the stated goal of U.S. officials is to make a substantial withdrawal of troops this year, it is not yet clear that the Iraqis will prove ready – politically or militarily – to take on the added responsibility. A Feb. 22 bombing of a Shiite shrine set off sectarian violence that has slowed the process of forming a permanent government in Baghdad, more than three months after December’s elections.

This week the outlook was altered by two developments. The Pentagon announced it was sending 700 more U.S. troops into Iraq from Kuwait, and it launched a large assault on suspected insurgent territory near Samarra, north of Baghdad.

The dispatching of extra troops to Iraq pointed up the problem of relying too much on Iraqi security forces during periods of heightened tension. But the helicopter-led assault near Samarra, which involved large numbers of Iraqi troops, showed that Iraqi forces are taking on bigger responsibilities, top U.S. officers said.

Lt. Gen. Peter Chiarelli, the No. 2 U.S. commander in Baghdad, said Friday that the goal is to turn control of 75 percent of the country’s territory over to Iraqi forces by the end of summer.