Hurricane Ivan clawed America's boggy Gulf Coast underbelly late Wednesday, knocking out power in southeast Louisiana and lower Alabama, lifting powerful waves onto the genteel island retreats of Mobile Bay and scattering nearly 2 million people in search of higher ground from the Florida Panhandle to New Orleans.

The maddeningly difficult-to-track storm, once expected to land as far east as Miami, punched its first hurricane-force winds onto the fragile marsh towns at the toe-tip of Louisiana's distinctive boot-shaped frame and by midnight EDT, Ivan was centered about 55 miles south of the Alabama coast, and was moving north at 12 mph. At least four people were killed in Florida and Louisiana. Ivan's hurricane-force winds targeted a region of seaside resorts, high-rise casinos, historic downtowns and oil refining behemoths. The imposing storm, which is expected to make its most emphatic landfall near Mobile early Thursday, built 12-foot waves that cascaded onto Alabama's barrier island shield and shut down the miles-long casino strip along Mississippi's Gulf Coast.

The 84-degree waters of the Gulf of Mexico helped strengthen the storm, keeping its winds at 135 mph. Ivan is just as powerful as Charley, which blew apart retirement towns on Florida's Gulf Coast last month, and is just as big as Frances, the hurricane that spread over nearly the entire state of Florida earlier this month. Ivan's hurricane- and tropical-force winds sprawled over an astonishing 300 miles, imperiling most of the Gulf Coast.

Oil and gas companies shut down their platforms in the Gulf in advance of the hurricane, and Energy Secretary Spencer Abraham told Reuters that the Bush administration would consider tapping the nation's Strategic Petroleum Reserve if supplies run short.

President Bush promised a quick and widespread relief effort.

"I told all four governors the people of this country are praying for their safety," Bush said. "We pray that the storm passes as quickly as possible without any loss of life or loss of property."

The storm inflicted its first damage in tiny Louisiana towns, such as Venice, that are connected only by a spindly, poorly lighted road to the more populated New Orleans area. In Plaquemines Parish, an area that fishermen and oil drillers have used for decades as a launching point for forays into the Gulf of Mexico, about 10,000 customers had lost power by 5 p.m., said parish president Benny Rousselle. By late evening, at least 40,000 were without power in Mobile.

Hurricane-force winds were recorded in Plaquemines Parish, even as the eye wall was still far off to the southeast. And -- disturbingly -- the strongest gusts were expected northwest of the eye, on the opposite side.

"We're on the good side, if you can call it a good side," Rousselle said. "But we're already hearing about roof damages, and trees blocking the roads. The levees have held so far, but I don't like to say that too loud."

After killing 68 on its rampage through the Caribbean, Ivan claimed its first American victims on Wednesday. Tornadoes spawned by the storm killed two people in Panama City, a resort town in the Florida Panhandle. In Louisiana, a cancer patient and a nursing home resident died in traffic while they were being moved to higher ground.

New Orleans was expecting some flooding from the outer edges of the storm, but nothing approaching the huge pounding that could happen if the city's below-sea-level streets took a direct hit from a major hurricane. Flooding fears prompted a mass exodus from the city on Tuesday, rivaling the evacuation ahead of Hurricane Georges in 1998 when an estimated 325,000 fled.

For those who stayed, Mayor Ray Nagin could offer little more than advice because relief agencies refuse to set up shelters in his city, fearing for the lives of their volunteers. Nagin called for a "vertical evacuation," urging stranded residents to seek the upper floors of buildings. He suggested they carry tools to cut their way out if they become trapped by rising waters.

Nagin, who was criticized Tuesday for not moving faster to allow cars leaving the city to travel on both inbound and outbound highway lanes, found himself in another controversy on Wednesday. After residents complained that he was allowing only hospital patients dependent on electricity to seek refuge in the Louisiana Superdome, he reversed himself and allowed the general public in.

Finding safe spots was a problem across the length of the Gulf Coast. A third of Mobile County's emergency shelters were full on Wednesday afternoon. Just to the west, Mississippi Gov. Haley Barbour (R) asked people to open their homes to family and friends.

"Hundreds and thousands of people live on the Gulf Coast and we currently only have shelters for 80,000," he said.

Mississippi's long history of hurricane scars is still visible, with broken boats from Hurricane Camille in 1969 sitting as tourist attractions in Gulf Coast towns. Camille -- which killed 262 people -- was one of three Category 5 hurricanes to hit the U.S. mainland since 1900. The others were Hurricane Andrew in 1992 and the unnamed storm that wiped out the overseas railway to Key West in 1935.

Hours before Ivan made landfall in southeast Louisiana, the storm's outer bands were tossing broken posts and shards of oyster boats onto Dauphin Island, at the mouth of Mobile Bay. More than 100,000 people were asked to evacuate Mobile County. Emergency managers believe almost half of those people -- far more than usual -- have fled north seeking higher ground.

"People are taking this more seriously than before because of the recent storms in Florida," said Lt. Richard Caytom of the Mobile County Sheriff's Department.

The evacuation response contrasted with Mobile's blase reaction to the approach of Hurricane Frederic, which killed five people in 1979. Mobile County Deputy Sheriff Rick Daves remembered waiting for Frederic in his squad car.

"We sat out at the high school under bleachers from 7:30 p.m. to 3 a.m.," he said. "A lot less evacuated then."

A major hurricane blast in Mobile could have a severe impact on the shipping industry. Mobile is the nation's 16th busiest port, accounting for 37 million tons of freight every year, most notably forest products and coal. On Wednesday, there was only one commercial vessel left in the port, but port spokeswoman Judith Adams said the storm was a serious threat to vital infrastructure.

"We've prepared as best we can, but now we need to keep our fingers crossed," she said. "We'll just have to wait and see."

Hers was a sentiment felt along 300 miles of coastline. On the evacuated Okaloosa Island in Fort Walton Beach, at the opposite end of the storm's likely path, George and Carol Edlund were among the last to leave Wednesday morning. The Gulf of Mexico churns a couple of hundred feet from the Edlunds' two-story brick-and-beige-shingle home.

"We're not stupid enough to try to weather it out," said George Edlund, 59, sweat dripping down his face and soaking his blue T-shirt.

The storm they are running from appears inclined to stay for a while. Forecasters expect that it will remain a hurricane for 12 hours after making landfall, moving slowly north, dumping as much as 20 inches of rain and threatening to flood Appalachian mountain towns.

Even before Ivan arrived on the Gulf Coast with the full brunt of its might, it was already ripping up piers on the Florida Panhandle and shredding barrier beaches south of Mobile.

"We're starting to get some pretty strong gusts," Adams said. "And this is just the beginning."

Roig-Franzia reported from New Orleans. Skipp is a special correspondent. Staff writers Michael Grunwald in New Orleans and Manny Fernandez in Pensacola, Fla., contributed to this report.

People run off the Pensacola Pier as Hurricane Ivan heads toward the Florida city with winds approaching 140 mph. Mandatory evacuations were in effect across the Panhandle as the state faced its third major storm in little over a month.After gathering as much as he could from his home in Dauphin Island, Ala., Jeff Deen, 52, wades through the island's flooded streets on his way to Mobile.Louisiana National Guard troops patrol New Orleans's French Quarter as Hurricane Ivan approaches the Gulf Coast.Several tornadoes -- including this one in Pamana City Beach, Fla. -- destroyed several homes and businesses. Rescuers were searching for trapped survivors.