"Obviously, the soldiers lack the necessary information about where to look and who to look for," said the government engineer, who declined to give his name in an interview during a sweep through his western Baghdad neighborhood last Monday. "There are too many houses and too many hide-outs."

American military commanders in Iraq describe the security plan they began implementing in mid-February as a rising tide: a gradual influx of thousands of U.S. and Iraqi troops whose extended presence in the city's violent neighborhoods will drown the militants' ability to stage bombings and sectarian killings.

But U.S. troops, Iraqi soldiers and officials, and Baghdad residents say the plan is hampered because security forces cannot identify, let alone apprehend, the elusive perpetrators of the violence. Shiite militiamen in the capital say they are keeping a low profile to wait out the security plan. U.S. commanders have noted increased insurgent violence in the Sunni-dominated belt around Baghdad and are concerned that fighters are shifting their focus outside the city.