With almost every rainstorm in the last nine years, Debbie Brannan got hints of why the curve in front of her house in Charles County was nicknamed Dead Man's Turn.

Cars hurtling out of control crushed her family's mailbox three times. Other vehicles smashed chunks from the brick posts at her driveway entrance. And there was the time when a teen-ager lost control of his car and came to a stop about 30 feet into a thick growth of brush and trees.

But nothing prepared Brannan for the sight on Thursday afternoon, when a rain-slick Dead Man's Turn claimed the lives of four members of a family from neighboring St. Mary's County, left the father in critical condition and killed a passenger in another car.

"It has gotten so that when it rains, I expect it to happen," Brannan said yesterday. "But {Thursday's} accident was bad, really bad. Now I know how that curve got its name."

The accident happened shortly before 3 p.m. on Rte. 5, not far from the St. Mary's County line. A brief shower left the heavily traveled road slick with patches of oily moisture and small pools of water.

A 1972 Ford Mustang carrying Patricia Day Smith and John Walter Smith III and their three children was headed north on Rte. 5, according to the Charles County Sheriff's Department, with John Smith III behind the wheel. John Smith apparently lost control of the car on the banked curve, the vehicle turned 180 degrees, and its rear end struck the front of a Nissan Sentra traveling south.

The collision ruptured the Mustang's gasoline tank, and the car exploded, said Sgt. Michael O'Toole, traffic safety coordinator for the sheriff's department.

Killed in the accident were Patricia Day Smith, five months pregnant, and her three children: Melanie April Smith, 6, Cassandra Blair Smith, 3, and Jacqueline Amber Smith, 7. John Walter Smith III, 31, was listed in critical condition in the intensive care burn unit of the Washington Hospital Center. The Smiths were from Lexington Park, Md., a St. Mary's County town about 25 miles from the accident.

Daniel Thomas Fitzgerald, 32, also of Lexington Park, who was a passenger in the Nissan, also was killed. His brother, Anthony Fitzgerald, 25, of Floral Park, N.Y., who was driving the Nissan, was listed in critical condition at the Prince George's Hospital Center.

A preliminary investigation indicated that the Smiths' car was traveling too fast for road conditions, O'Toole said. No one in either car was wearing a seat belt, he said.

The stretch of Rte. 5 where the accident occurred is about one-tenth of a mile long, and, at least when the blacktop on the road is dry, negotiating the banked curve is not unusually difficult. At the approach of the turn, the posted speed limit drops from 55 miles an hour to 50, and a yellow and black sign warns of an impending curve in the roadway.

Longtime residents of Hughesville, near the accident site, and the sheriff's department agreed that Dead Man's Turn was more treacherous before the early 1970s, when the State Highway Administration, as part of a widening of Rte. 5 through the area, increased the total number of lanes from two to four, made the turn less sharp and banked it.

William A. Bridgette, 51, who owns a garage that has operated about one-half mile north of the curve since 1946, said the stretch of road has had the nickname "for as long as I can remember."

In his teens, Bridgette said, his father sent him to retrieve trucks that unsuccessfully traveled the curve. Later, as a volunteer emergency rescue worker, Bridgette picked up the curve's victims in an ambulance.

"So many people have been killed there," he said. "But the accident rate has slowed down since the state made the curve less sharp."

The State Highway Administration said yesterday that the accident on Thursday was the first involving fatalities for the small stretch of Rte. 5 since 1979. The last reported accident on that short strip was in 1984.

Joe Beuchert, 22, a Hughesville volunteer firefighter, said that Charles County emergency dispatchers send vehicles to Dead Man's Turn, instead of identifying the section of road by its mile marker, as is the usual practice.

"Things have improved," Beuchert said. "We haven't had a fatality there in years. But unfortunately, with the rain {Thursday's accident} made up for it in one fell swoop."

For acquaintances of the victims, the curve's tragic history provided little solace. John Smith III, a lab worker at the Baltimore Gas & Electric nuclear plant in Calvert County, had always "put aside time for his family," said Mary Quarles, his aunt.

Patricia Smith drove a school bus for Lexington Park's two elementary schools and told a coworker about her pregnancy on June 17, the last day of school. "She was excited about it, and we were very happy for her," said Maria Owens, a secretary at Lexington Park Elementary School.

The three children were attractive, friendly, affectionate and headed for high achievement in school, officials and relatives said. "They'd always come in the office and give you a hug and a kiss," Owens said.