A tanker truck carrying 1,600 gallons of propane fuel turned over and caught fire yesterday on the Capital Beltway south of Largo, forcing the closure of the highway for about three miles and the evacuation of hundreds of area residents.

The accident occurred shortly before 1 p.m., and the highway remained closed into the early morning while fire officials, fearing that the tanker might explode, waited for the fire to burn out. When it did, about 2:30 a.m., officials said the road would not reopen before 5 a.m. No serious injuries were reported because of the fire and evacuation, but some elderly evacuees suffered from the heat, which reached temperatures of 96 degrees and caused area schools to close early. Details, Page D1.

Thousands of motorists were trapped on the Beltway for several hours because of the fire, and others sat for hours in traffic that moved at a crawl.

It was not immediately clear when residents would begin returning to their homes.

While the fire was still burning, one firefighter explained that "The only thing to do now is to let it burn . . . . We're just sitting back waiting."

Fire department spokesman Tony DeStefano said, "It's like a pilot light out there now. There's no sense risking life by sending them out to that tanker." In the meantime, more than 400 residents were ordered out of the area. About a third of them were taken to makeshift shelters at two area schools, which had been closed early because of the sweltering heat.

"Sixteen hundred gallons of propane has the ability to cause a very, very big explosion," said Fire Chief Jim Estepp. "We're talking in the neighborhood of 2,000 degrees. It's at the top of the scale of flammability." The driver of the truck, identified by fire officials as Jerry Gammon, 31, from Halethorpe, Md., received minor injuries and was treated and released from Prince George's General Hospital.

The driver scrambled out of the cab immediately after the accident, DeStefano said.

The accident occurred when the tanker truck, owned by Poist Gas Co., blew a tire and turned over on the southbound lanes of the highway. DeStefano said the flames were along the lines used to load and unload the fuel, but that it was unclear if they had ruptured or if seals had been broken, causing the propane to leak out. The extreme heat and the threat of an explosion prevented firefighters from getting close enough to determine the exact source of the fire.

Firefighters monitored the fire from a command post a half-mile from the crash site at Ritchie Marlboro Road. As many as 18 county fire trucks and 75 firefighters, the equivalent of the response to a three-alarm fire, were stationed at four locations in response to the incident, DeStefano said.

Police blocked off the Beltway, the busiest highway in the Washington area, between Central and Pennsylvania avenues, a stretch of about three miles. Traffic on other roads in the area was backed up as much as three miles in each direction, according to state police.

Firefighters, police and volunteers went door-to-door in neighborhoods within a mile of the crash, telling residents to grab shoes, medication and their wallets and leave their homes immediately. The evacuees, many of them elderly residents of a mobile home park, were taken in a half-dozen school buses and ambulance buses borrowed from Andrews Air Force Base.

"I was scared," said 67-year-old Mary Hennen, who was making a peanut butter and jelly sandwich when she was told to leave her two-bedroom mobile home in the Fernwood Mobile Home Park about 100 yards from the interstate.

She was evacuated with more than 125 others to Arrowhead Elementary School, where the Red Cross served cafeteria hamburgers to the temporarily homeless. They were later transferred by bus to Largo High School, where officials decided that they would be more comfortable for a long stay. "I'm still scared," Hennen said midway through the afternoon. "I don't want anything to happen to my home."

Thirteen-year-old George Hickman, an eighth grader at Walker Mill Middle School, was headed home on a school bus when he was told he could not go to his Largo home in one of the evacuated areas.

"I haven't been able to even call my parents," he said. "I hope they'll show up here sometime."

The accident followed by less than a month a crash of a truck carrying corrosive chemicals on the Beltway in Northern Virginia that forced the evacuation of 630 people from their Fairfax County homes. Two years ago, a tractor-trailer carrying 8,500 gallons of flammable gas overturned on the Beltway near the Baltimore-Washington Parkway, causing the evacuation of 250 homes.

After yesterday's accident, traffic was rerouted onto side streets and back onto the Beltway farther from the crash site, but for most commuters, the rush hour lasted several hours with cars stacked bumper-to-bumper. "The traffic was backed up so heavily . . . I was running out of gas," said Shirley Williams, a Montgomery County teacher on her way home from Rockville to Brandywine. She said she had been in her car for two hours.

Firefighters prohibited anyone from getting within 2,500 feet of the tanker, even hours after it turned over. Only two firefighters from the county's hazardous materials response team approached the burning, sausage-shaped, yellow-and-white truck to take pictures.

While drivers overheated in their stalled vehicles, evacuees at Arrowhead Elementary also suffered through the heat. The school, with only one air-conditioned wing, was a chaotic scene. Children roamed the halls and played on the lawns while elderly evacuees, some in their bedclothes, waited for word on when they could return home.

A makeshift infirmary was set up in the air-conditioned wing of the school; late in the afternoon, five people were being treated by a Red Cross nurse.

Staff writer Kim Chappell contributed to this report.