BAGHDAD, Iraq — The United States is steadily losing ground to the Iraqi insurgency, according to every key military yardstick. A Knight Ridder analysis of U.S. government statistics shows that through all the major turning points that raised hopes of peace in Iraq, including the arrest of Saddam Hussein and the handover of political sovereignty at the end of June, the insurgency, led mainly by Sunni Muslims, has become deadlier and more effective. The analysis suggests that unless something dramatic changes, such as a newfound will by Iraqis to reject the insurgency or a large escalation of U.S. troop strength,...