Prince George's County resident Synetra Mendheim and her father, Terry, had noticed the car as they headed toward her white Mazda Millenia that Sunday morning, but they thought the men inside were waiting for a parking place.

It was 3:30 a.m., and Synetra Mendheim, 25, was going to Reagan National Airport for a flight to South Africa, where she would join other missionaries from her church to work with young AIDS patients. Terry had driven up from Virginia Beach to drive her to the airport. The plan was for Terry, in his late-model Mercedes, to follow Synetra to her mother's house nearby in Fort Washington, where she would drop off the Mazda and give one last kiss to her baby daughter, Kaylan, who had spent the night at her grandmother's house.

As Synetra Mendheim reached for her keys, three car doors opened and a shotgun cocked.

"Get on the ground! Get on the ground!" a man shouted, pointing the gun at her father. Synetra froze. Terry got on the ground and called her name.

"I thought, 'This cannot be happening,' " Synetra Mendheim said in an interview. "When my dad called my name, it snapped me back. I lay on the ground in an almost fetal position. I was so scared. I just wanted to curl into a ball so that I could protect myself."

The April 24 carjacking, in the 7200 block of Jaywick Avenue in Fort Washington, was among 337 such crimes reported in Prince George's County as of June 30, a 47 percent jump from the 229 carjackings reported at the same time last year. In 2004, Prince George's reported the highest number of carjackings in Maryland: 563, compared with 492 for all of the state's other jurisdictions combined.

As police officials try to combat the problem, some county residents look over their shoulders in parking lots and curtail activities for fear that they will become the next victim. They avoid gas stations and limit nighttime trips to the grocery store and mall. They dig for their keys before they leave their offices and watch who lurks near their homes before they pull into their driveways or parking spaces.

"When I come home, I keep my car doors locked while the garage door goes down," said Mitchellville resident Ann Powell, a professor at Gallaudet University. "I don't get out of my car until the garage door is all the way down."

Mark Ricks, 38, of Laurel, a Web site designer, said he is careful about driving in areas where a number of people loiter, parks where other people can see him and is more apprehensive in parking garages.

"And I make it a habit to lock my doors when I first get into my car -- even before I put on my seat belt,'' he said. "I'm not going to say that I take an extra minute when going into the parking lot to look around, but it is kind of scary."

Law enforcement officials say they are working on solutions and acknowledge that concerns about carjacking, as well as other violent crimes, have affected some residents' quality of life.

"Carjacking is one of the highest priorities, along with homicides and other violent crimes," said Vernon R. Herron, the county public safety director. "It's terrifying. When someone is carjacked at gunpoint or by force, they are traumatized. It is something they will always remember.''

Synetra Mendheim, who works as a receptionist at a Northwest Washington law firm, worries when she returns home from Bible study classes. After a recent evening out with girlfriends in Georgetown, she made all of them spend the night when they got back to her apartment for fear that they would meet up with carjackers in the parking lot. She was especially worried because police said that another man was carjacked a few minutes after she was on April 24 and that several other armed car thefts have occurred in the area.

"We got back to my apartment, but then we talked and hung out, so by the time they were ready to leave, it was almost 3 a.m., about the time I got carjacked," she said. "I said, 'Nobody is going anywhere. You're all staying right here.' "

She and her sister, Charlise Mendheim, 28, who shares the apartment, also refuse to get out of their cars if anyone is nearby on foot or in a car when they get home.

"We have a pact that if we see anybody, we ride around and then come back," said Synetra Mendheim. "We don't get out of the car while anybody is waiting and while anybody is standing around."

Averyl Bailey, 33, whose 2002 gold Land Rover Discovery was carjacked in the 8600 block of Devon Drive in Fort Washington as she returned home from choir practice June 20, said she no longer checks her mailbox at night. She was at the box, down the hill from her home, about 10:45 p.m. when a red car pulled up and three men approached her -- two of them armed with handguns.

Police are investigating the case as possibly connected to a gang of violent car thieves suspected in at least three carjackings in Clinton and Hyattsville since June 18. At some scenes, the men left in a silver Nissan Altima, which has subsequently been recovered in the District.

Detectives are also investigating carjacking as the motive in at least one unsolved homicide. They declined to identify the case.

Herron said the county's carjacking victims "cross every socioeconomic line." Victims who have been carjacked in recent months include an off-duty police officer whose silver 1995 Chevrolet Caprice was stolen at gunpoint about 6 p.m. June 18 in the 8000 block of Mike Shapiro Drive in Clinton.

In several cases, the carjackers have abducted car owners and resorted to violence. In one recent carjacking, a man who came to the aid of his girlfriend was shot. In March, a man standing next to his 2000 Toyota Avalon in the 2700 block of Crestwick Place in Suitland was abducted by the carjackers, driven to several locations and placed in the trunk. Police believe the carjackers committed several robberies while the victim was in the trunk. On May 5, Prince George's police chased a carjacking suspect into Southeast Washington and fatally shot him.

Cars have been recovered in many of the cases. The cars belonging to Bailey, the off-duty police officer and Synetra Mendheim have been recovered. Police also recovered a 2000 Chrysler 300M that was carjacked in the same parking lot on Jaywick Avenue a short time after Mendheim was robbed of her car. Two men have been arrested in the heist of Mendheim's car, and police told her that they were looking for three or four other suspects.

Synetra Mendheim is relieved that her story had a happy ending. When Terry Mendheim could not produce his wallet, his daughter pleaded with the robbers. Frantically searching for a reason, she said: "Please don't shoot him. He doesn't live here."

When the carjackers saw her curled in a ball, one of them kept snatching at her legs until she lay flat. She prayed, and they eventually drove away, taking her backpack and her luggage, which included a suitcase of jackets donated by church members for the children in South Africa.

Terry Mendheim checked his daughter for injuries, then made her a pledge. "You're still going," he said of the missionary trip. "I don't know how, but you're still going."

As police investigated the case, Synetra Mendheim's church, the Soul Factory in Forestville, mobilized to get her another passport and plane ticket. She went to Africa as planned, two days after the carjacking.

Synetra Mendheim was the victim of a carjacking in the parking lot of her Fort Washington apartment. "I was so scared," she says.