Roma Campanaro and two friends were returning home from Georgetown early on Aug. 5 when they picked up a pair of hitchhikers on Rte. 270 in Montgomery County -- a girl with a baby in her arms.

"She said her husband had been beating her and that she was going to see her mother in Pennsylvania," said Campanaro, an 18-year-old college student from Montgomery County. "She was very convincing."

Sympathetic to the girl's dilemma, Campanaro and the others decided to drive her to her destination, Breezewood, Pa., a town two hours away. It was not until later that they learned that the hitchhikers may have been 14-year-old Tammy Lynn Giles, a habitual runaway from Waldorf, Md., and Michael Justin Fitzgibbon, the 21-month-old child for whom she had been baby-sitting.

Almost two weeks have passed, and sheriff's deputies and police officers from southern Maryland to Pennsylvania are still searching for the child and the baby sitter. On Thursday, the Maryland state's attorney filed juvenile charges of kidnaping and abduction against Giles; a nationwide alert was already in effect.

"It's like she vanished into thin air with my son," said Michael's mother, Sharon Fitzgibbon, 34, who works for a real estate company in Waldorf. In a tearful telephone interview from Pittsburgh, Fitzgibbon said she intends to remain in Pennsylvania -- where police have confirmed three recent sightings of Giles, but none of the boy -- until her son is found.

By all accounts, Tammy Giles, a short blond girl with round cheeks and a self-confident air, is a troubled teen-ager often attracted to an older, streetwise crowd, said Charles County Sheriff's Sgt. Casey McDevitt. In the past 1 1/2 years, she has run away from home 22 times, to places as far away as Tennessee, Texas and California, McDevitt said, but she had always returned after a few days. Police say she may have gone to Pennsylvania intending to meet a male companion who is to be released from a state prison near Pittsburgh on Sept. 13.

McDevitt said Giles does not have a criminal record. He said that she "is not a violent person" and that police do not believe she intended to harm the child.

"As far as we can tell, she comes from a good family, a nice home," McDevitt said. "They've just had a lot of problems with the girl." Her parents, who have avoided the media since her disappearance, could not be reached for comment.

Giles volunteered to baby-sit for Michael on the night of Aug. 4 when the child's 15-year-old sister, who had been given that responsibility, wanted instead to spend the night with a friend, according to police and the child's parents. Sharon Fitzgibbon, a single mother, was away for the weekend. She described Giles as a school acquaintance of her daughter who had visited the Fitzgibbon home only once before.

"We thought she Michael's sister was old enough to keep him, but she wasn't," said Bob Fry of Waldorf, Michael's father. "She's a pretty tough little kid, but she's been going into a depression a lot about this."

Police say Giles and the baby disappeared sometime late Sunday night or early Monday morning, Aug. 4 or 5. Fitzgibbon thinks that Giles might have figured that motorists would more readily pick up a young girl who had a baby. Fry has another theory: "We understand that she really took to Michael," he said. "Maybe she thought love with a baby is reciprocated."

Campanaro and her friends apparently happened upon Giles and the child at 2 a.m. Aug. 5. She said Giles, who wore heavy makeup, was dressed in jeans, running shoes and a blue-and-white sweatshirt; the boy was in pajamas and a sleeping-bag blanket. Giles also carried two duffle bags.

Once inside the car, Giles introduced the baby as Michael and herself as Patty, which happens to be the name of Michael's sister.

"We never thought she wasn't his mother," Campanaro said. "I never asked her age. I didn't want to pry."

During the drive, Giles talked matter-of-factly about her mythical husband, Campanaro said. She said they initially had lived in Pennsylvania but had recently moved to Waldorf to work. She said she decided to return to Pennsylvania after her husband, in a fit of anger, had slashed the tires on her car, Giles said. In Pennsylvania, she said, she intended to settle down, get a job and make a new life for herself and her son.

At one point in the drive, Campanaro and a female friend commented admiringly on a model's figure while leafing through a fashion magazine. "I looked just like that before Michael was born," Campanaro said Giles told the women.

"The baby was so friendly," Campanaro said. "We fell in love with him. He seemed very comfortable with her, but we were a little concerned about him and the fact that she seemed so young. Once, when she went to the bathroom, we talked about it. But one of my friends pointed out that she had a good head on her shoulders and she did seem very clever."

Campanaro said Giles told them to take her to the Breezewood bus station, where she would telephone her mother to pick her up. She declined the offer of a ride to her mother's home, saying her mother would be angry if she knew Giles had been hitchhiking. Nevertheless, Campanaro and her friends waited at the bus station with Giles and the child for an 1 1/2 hours. Giles went away to make a telephone call, Campanaro said, but did not seem anxious for them to leave.

"She really seemed to take on the mother role," Campanaro said. "Michael was playing around a video machine in the bus station and she'd say, 'Michael, get away from there,' and he obeyed."

In retrospect, however, some aspects of Giles' behavior toward the boy were disturbing, she said.

"To get his attention, she'd say, 'Michael, Mommy's going to leave you,' " Campanaro said. "And then she'd pretend to walk away and he'd look up. She did this a lot, more times than I can count, and it was kind of weird.

"There was another thing during the drive that bothered us afterwards," Campanaro said. "She said she was afraid somebody might get Michael and try to put him in one of those child porno rings."

Campanaro and her friends left the bus station at dawn. Michael kissed them goodbye, she said. A few nights later, they heard about the baby sitter and baby's disappearance through news reports, and they contacted police. Sgt. McDevitt said that the hitchhikers were Giles and the Fitzgibbon child.

Fry, Michael's father, said he has made a trip to the Pittsburgh area, where he found a truck stop waitress who recalled seeing Giles later that same week. Also, he has visited Giles' parents in search of clues.

"At first, they treated it like, 'So, she's run away again,' " said Fry, 43, a construction superintendent. "I understand that. You got a kid who runs away once every three weeks and always comes back -- what can you do? They said that, in the past, they've gone to the county juvenile officials and tried to get help for her. But they were told nobody could do anything until she commits a crime."

Fry described his son as "an outgoing little guy" who loves to play with balls and, so far, talks only baby talk -- "moomoo" for milk, "coco" for cookies.

"I lay awake at night worrying about him," he said.

He and Fitzgibbon say they feel no ill will toward Giles.

"I just want her to bring him home," Fitzgibbon said. "Please."