FALLUJA, Iraq, Monday, Nov. 8 - Explosions and heavy gunfire thundered across Falluja on Sunday night and Monday morning as American troops seized control of two strategic bridges, a hospital and other objectives in the first stage of a long-expected invasion of the city, the center of the Iraqi insurgency. Hours earlier, Prime Minister Ayad Allawi, faced with an expanding outbreak of insurgent violence across the country, formally proclaimed a state of emergency for 60 days across most of Iraq. The proclamation gave him broad powers that allow him to impose curfews, order house-to-house searches and detain suspected criminals and...