Hurricane Katrina pounded the Gulf Coast with devastating force at daybreak on Monday, sparing New Orleans the catastrophic hit that had been feared but inundating parts of the city and heaping damage on neighboring Mississippi, where it tossed boats, ripped away scores of roofs and left many of the major coastal roadways impassable.

Packing 145-mile-an-hour winds as it made landfall, the storm left more than a million people in three states without power and submerged highways even hundreds of miles from its center.