This could be the storm that everyone feared.

Hurricane Katrina, one of the strongest storms ever to threaten the United States, carved a path toward the Gulf Coast yesterday, packing 165-mph winds and forcing the evacuation of hundreds of thousands of residents of New Orleans and the region.

All lanes on interstate highways in the New Orleans area were given over to outbound traffic, as people made a last-ditch attempt to escape the massive Category 5 hurricane. Traffic was bumper-to-bumper as far away as Jackson, Miss., more than 180 miles to the north. Thousands of people who could not get out of town lined up outside the 70,000-seat Superdome, hoping to take refuge in the home of the New Orleans Saints professional football club.

As a much weaker storm, Katrina was responsible for nine deaths in South Florida. According to David Miller of the National Hurricane Center, it was on track to make landfall late this morning in southeastern Louisiana, a low-lying area that experts say is especially ill-suited to withstand a direct hit from a powerful storm. New Orleans is considered a disaster waiting to happen -- a city mostly below sea level, practically surrounded by water, artificially kept dry by pumps and levees, and rapidly losing its natural storm protection.

If Katrina makes landfall as a Category 5 storm -- winds greater than 155 mph -- it would be only the fourth to do so in the United States since records have been kept.

"This is a very large hurricane, a very powerful hurricane," said Lixion Avila, a forecaster with the National Hurricane Center. "Wherever you have the eye of this system, you are going to have a potentially catastrophic disaster there. This is the worst-case scenario for a hurricane."

The National Weather Service issued a hurricane warning from Morgan City, La., to the Alabama-Florida border, cautioning that the storm could march ashore anywhere in that region. Officials warned of a "potentially catastrophic and life-threatening" direct strike to New Orleans. Flooding could send water as high as 28 feet above normal tide levels, and as much as 15 inches of rainfall was expected in hard-hit areas, the weather service said.

New Orleans Mayor Ray Nagin ordered the mandatory evacuation of the city's 485,000 residents. Officials acknowledged that tens of thousands of residents and tourists would be unable to leave. With the airport closed, the city organized buses to transport those left behind to 10 emergency shelters and encouraged people to bring supplies and food for a three- to five-day stay. Three nursing home patients died during the evacuation, according to an Associated Press report.

"This is a once-in-a-lifetime event," Nagin said at a televised news conference. "The city of New Orleans has never seen a hurricane of this magnitude hit it directly. . . . We are facing a storm that most of us have long feared."

Officials said Katrina's wrath could easily surpass the devastation caused in 1965 by Hurricane Betsy, the most punishing storm to hit southeastern Louisiana. That storm killed 75 and caused $7 billion in damage when southern Louisiana was less populated and less exposed.

Louisiana Gov. Kathleen Babineaux Blanco (D), with Nagin at the news conference, said, "There doesn't seem to be any relief in sight."

Todd and Anne Crosley bundled their three small children and as many valuables as they could carry into their car yesterday and began the 225-mile drive to a hotel in Vicksburg, Miss. The Crosleys' home in the New Orleans suburb of Kenner is two blocks from Lake Pontchartrain, and the family had fled hurricanes at least twice before.

"My gut this time tells me that it's going to be bad," said Todd Crosley, 35, who co-owns two area restaurants. "Going into the busy time of year with tourism in New Orleans, it could really decimate things downtown, and our businesses rely on that.

"Economically, New Orleans is unstable as it is. Throw a hurricane in the mix, where everyone shuts down for a couple of weeks, it just could really be devastating."

The usually bustling French Quarter was nearly deserted yesterday afternoon. Stranded tourists packed the lobbies of high-rise hotels, which were exempt from the evacuation order to give people a place for "vertical evacuation."

Real estate agent Mary Lind, who lives in a 174-year-old pink brick house in the French Quarter, was staying, much to her family's chagrin.

"My son's having a fit," she told the Associated Press. "We're kind of a different breed of people down here, people in the Quarter. Heck, if we can put up with Mardi Gras, we can put up with a hurricane."

Julie Paul, 57, sat on a porch yesterday with other residents of a poor neighborhood in central New Orleans who said they had no way to leave town. "None of us have any place to go," the AP quoted her as saying. "We're counting on the Superdome. That's our lifesaver."

The American Red Cross said it had set up 35 kitchens in Louisiana, Mississippi and Alabama that could serve 700,000 meals a day. Meanwhile, President Bush declared a state of emergency in Louisiana and Mississippi, making it easier for federal agencies to coordinate relief efforts with states and localities.

"We cannot stress enough the dangers this hurricane poses to Gulf Coast communities," Bush said.

At 1 a.m. Eastern time, Katrina's eye was about 90 miles south-southwest of the mouth of the Mississippi River and 150 miles south-southeast of New Orleans. The storm was moving toward the north-northwest at about 10 mph and was expected to turn toward the north.

Jake Ladner, 30, and Susan Smith, 27, fled their New Orleans home yesterday and planned to hunker down with Ladner's parents in Wiggins, Miss., about 90 miles away. "I'm terrified I won't have a home to go home to," Smith said.

Brooks and Cindy Bamburg also headed north, afraid their home near Biloxi, Miss., would be inundated by surging waters. "We're next to the bayou," said Brooks Bamburg, 59, a pharmacist. "We're 17 feet above the water.It's going to be bad."

New Orleans is especially vulnerable to a hurricane's fury because the city sits six to eight feet lower than the surrounding waters of the Mississippi River, Lake Pontchartrain and the Gulf of Mexico. And it is sinking lower every year.

The levees that harnessed the Mississippi and helped make New Orleans one of the world's busiest ports and a thriving center of the oil and gas industry also have prevented the river from spreading sediment around its delta. As a result, southern Louisiana is slowly sinking into the encroaching Gulf, losing about 24 square miles of coastal marshes and barrier islands every year. Those marshes and islands used to help slow storms as they approached New Orleans; computer simulations have suggested that the loss of them will increase storm surges and waves by several feet.

"If you can picture sort of a soup bowl, the city is located in the middle," said Gregory Stone, director of the Coastal Studies Institute at Louisiana State University in Baton Rouge. "And once the levees -- sort of the perimeter of the bowl -- are breached or overtopped, then that water gets in there and just can't get out. . . . It's like filling a bucket up with water. This is probably the worst-case scenario that we've all been very, very worried about for quite some time."

Nagin said Katrina's predicted storm surge would probably overwhelm New Orleans's levees. And the city's pumps -- capable of removing only an inch of water every hour under normal conditions -- require electricity, often the first casualty in any hurricane. If Katrina does slam into New Orleans, experts say the city could be underwater for weeks or months, creating a toxic soup of chemicals, rodents, poisons and snakes.

The storm also could contribute to rising gasoline prices by curtailing refining activity in the region. Already, oil companies have shut down facilities that produce an estimated 1 million barrels a day. The last Category 5 hurricane to make landfall in the United States was Andrew, which left 43 people dead and caused $31 billion in damage when its 165-mph winds tore across South Florida in 1992. Hurricane Camille killed 256 people along the Mississippi coast in 1969, and the 1935 Labor Day hurricane killed hundreds when it hit the Florida Keys.

Katrina formed Wednesday over the Bahamas as a tropical depression. By Thursday it was a Category 1 hurricane with 80-mph winds, flooding neighborhoods in South Florida and leaving more than 1 million homes and businesses without electricity. The storm then moved over the Gulf of Mexico and, nourished by warm waters, angled toward the Gulf Coast as it steadily rose in intensity.

Whoriskey reported from Wiggins, Miss.

Jeff Johnson holds his daughter Kayla in the nearly deserted French Quarter as New Orleans residents fled inland to escape Hurricane Katrina, projected to land this morning.Drivers and passengers wait outside their cars as traffic snarls on the interstate highway leaving New Orleans after Mayor Ray Nagin ordered the city evacuated.A Louisiana National Guard member holds back New Orleans residents seeking storm shelter at the Superdome.