Hearing the lessons of Katrina in the growling winds, hundreds of thousands of remaining residents of south Texas and southwestern Louisiana fled their homes or hunkered down for the duration as they awaited Hurricane Rita's expected arrival in this gritty oil-patch region Saturday morning.

Weakened since its peak but still packing winds of 120 mph, Rita dumped torrential rains on coastal towns as it veered north from its path toward Houston, heading instead for the Texas-Louisiana border.

The Category 3 storm brought misery even before it hit land, inundating the battered city of New Orleans with fresh floodwaters as levees weakened by Hurricane Katrina failed to hold off another assault.

Outside Dallas, as many as 24 elderly evacuees from the Houston area were killed Friday morning when their bus burst into flames. The driver and some passengers frantically tried to save others before oxygen tanks used by many of the riders exploded. The cause of the fire is unknown.

Nearly 3 million people are estimated to have fled the coastline of south Texas and southwest Louisiana in a two-day evacuation that caused monstrous traffic jams, which were worsened by hundreds of vehicles that ran out of gas. Although traffic had lightened noticeably by Friday afternoon, it was still bumper-to-bumper outside Houston as remaining residents headed north to Dallas and beyond.

Determined to avoid the sluggish response to Katrina that stranded thousands in New Orleans and battered President Bush in the polls, the administration readied thousands of federal troops and massive numbers of military vehicles for Rita. Bush flew on Friday to Northern Command headquarters in Colorado Springs in advance of the storm's landfall.

In Beaumont, Port Arthur and other refinery towns in the expected path of the storm, nearly all streets and homes were empty as authorities prepared for a storm surge as high as 20 feet and as much as 25 inches of rain once Rita barrels ashore early Saturday.

Although a mandatory evacuation order had been issued for the area, authorities were not trying to force people from their homes. Some, despite the increasing urgency of radio and television reports, refused to believe they were in danger.

"You can't run from the good Lord," mused Eugene Henry, 62, as he sat sipping beer with two friends on his stoop in Port Arthur. A few blocks from his house, a 14-foot levee was all that kept the water from the town.

But authorities estimated that almost all of the other quarter-million people living in Beaumont and Port Arthur had left. Hospitals and nursing homes were mostly empty. Inmates were taken from the sprawling, fenced-in prison complex south of Beaumont and put in a crowded -- but higher -- county jail.

"We don't have the resources to force people out of their homes," Beaumont police spokesman Crystal Holmes said. "But we have made it very clear to them that when we have to take shelter, all emergency services will stop. If people are trapped or if there is a fire in the city, no help will be coming. The consequences of staying could be death."

Police and rescue personnel settled for the night in fire stations and hospitals, although firefighters in Galveston battled a blaze that engulfed three buildings. Beaumont loaded hundreds of ambulances, firetrucks, dump trucks and police cars onto two troop transport ships to be ready for quick offloading after the storm.

Shrimp boats and tugboats that were caught by the shift of the storm's path retreated from the Gulf of Mexico to Sabine Lake and up a narrow shipping channel toward Beaumont, seeking refuge.

"You got storm surge. You got flooding. You got spinoff tornadoes, and you got hurricane winds coming," Beaumont Port officer Renee Utley said. "You'll get a lot for your money with this storm."

Port Arthur, a town of about 56,000 boxed in by water on two sides, seemed otherwise deserted. All stores were closed, buildings boarded. A Texas officer said a few law enforcement officers planned to ride it out in a local hotel.

By mid-afternoon, the skies had taken on a sinister tone, with dark gray clouds rolling to the horizon. The first rains pelted down, carried by gusts of wind, the precursors of the storm to follow.

"I've been through them before," said Brian Williams, 33, an officer with the Texas Alcoholic Beverage Commission, one of many agencies pressed into emergency service. "This is just another storm." He paused, then added, "Well, this might be bigger than that."

The Texas homeland security director, Steve McCraw, said some low-lying communities, such as Beaumont and Port Arthur, could be underwater for as many as seven days.

If the storm stalls after it makes landfall, and moves slowly, McCraw said, heavy rains and ensuing tornadoes could affect 80 counties and 11 million residents.

The Beaumont and Port Arthur area has a large number of petro-chemical and chemical plants. McCraw said companies worked with state officials to shut down and secure facilities, but not all are shuttered.

"Some plants need to stay open," he said, declining to provide details. "They're vital to national security."

During the hours of Rita's fullest impact -- expected early Saturday -- Texas disaster officials warned there will be little that can be done. But Jack Colley, state coordinator for the Governor's Division of Emergency Management, said the state was taking advantage of the last few hours before the winds become too strong to move food and water into the Houston area.

"We are fully prepared for Hurricane Rita to strike this Texas coast," Colley said.

Colley also said it would be up to local officials to tell people when they can return to their homes. "That is at the discretion of local elected officials," he said. "The same elected officials who can order mandatory evacuations can decide when to let people back in."

Texas has called more than 10,000 National Guard troops to respond to Rita, out of a total of 20,000 soldiers and airmen. About 5,800 Texas National Guardsmen are deployed overseas.

Texas and Louisiana have also asked for a total of 25,000 active-duty troops, but a spokesman for Joint Task Force Rita said specific active-duty units had not yet been identified.

Army Lt. Gen. Robert Clark, head of Joint Task Force Rita, based at Fort Sam Houston in San Antonio, said military units are ready to move in as soon as conditions allow Saturday.

The task force's first priority will be search and rescue, particularly by air and executed by military as well as private and media aircraft. To keep the helicopters from flying into one another, the operation will use an airspace management system developed in the wake of Katrina.

"We really learned lessons in that operation, and we're applying them today," Clark said.

Hotels and shelters in Dallas were at or near capacity. All American Red Cross shelters were full Friday night, with 2,700 people housed in the convention center, Reunion Arena and three other facilities in the area. The city was housing evacuees at a former jail, which was also full.

Just as New Orleans was beginning to dry out, haul away debris and turn on the lights, the city was again deluged as water rushed over and through recently repaired levees, flooding the Ninth Ward neighborhoods that were submerged by Katrina.

Around 9 a.m., water began pouring over a 100-yard span of the temporary wall installed along the Industrial Canal. A hole about 30 yards wide then blew open. Water topped the temporary floodwalls in at least two other locations, creating an eerie rerun of the scenes of nearly one month ago when floodwaters submerged cars, trees and homes. By late Friday afternoon, the lower Ninth Ward appeared to have more than three feet of water rushing toward St. Bernard Parish.

"It's back to what you call ground zero," said Mark Castillon, an officer candidate with the Louisiana National Guard.

Army Corps engineers attempted to plug one smaller break but were unsuccessful. Maj. Gen. William B. Caldwell IV, commander of the 82nd Airborne Division, said helicopters will be used to drop sandbags again -- but not until the torrential rains and heavy winds stop.

With a full day of heavy rain and winds, the deserted city was again littered with tree limbs and downed power lines; many of the portable toilets brought in for Katrina were knocked over like children's building blocks.

To the west in Lake Charles, the city was almost empty as thousands fled in advance of Rita.

"There's nothing really to compare to this," said Sgt. Wendell Carroll of the Calcasieu Parish Sheriff's Office in Lake Charles. "After Katrina, everybody's thinking about hurricanes has changed. At least now, hurricanes are being taken more seriously. We're ready and waiting."

The approach of Rita has also put a huge strain on Lafayette, La., a center of Cajun culture, where emergency officials scrambled to send Katrina evacuees to shelters farther north to clear space for the onslaught of Rita evacuees.

Lt. Gen. Russel L. Honore, the federal Katrina chief overseeing Rita preparation efforts from Lafayette, told reporters that hundreds of troops are staging in Baton Rouge but that trucks and helicopters will not begin going into damaged areas until winds get below 40 mph.

"Pray," Honore advised the residents of southwest Louisiana. "A little prayer right now will work, hopefully."

Eggen reported from Washington. Staff writers Ceci Connolly in New Orleans, Blaine Harden in Houston, William Booth in Dallas, Steve Hendrix in Austin, Manuel Roig-Franzia in Lafayette, La., and Ann Scott Tyson in Washington contributed to this report.

Members of the Army National Guard and the Air National Guard take sick patients and the elderly to military aircraft in Port Arthur, Tex., for relocation.Levees in New Orleans's Ninth Ward were unable to contain the new surge of water produced as Rita approached.A fire burns in downtown Galveston, Texas as Hurricane Rita approaches the coast Friday, Sept. 23, 2005. As the storm approached, at least three buildings caught fire in the city's historic Strand District of nightclubs, shops and restaurants. It was unclear what caused the blaze, but a fallen electrical pole was lying on one of the buildings. High winds whipped the flames from structure to structure. (AP Photo/David J. Phillip)