The last time Loreli Smith saw her baby, the 2-day-old infant seemed safe in the arms of a hospital staff member.

But despite her uniform, the woman who lifted tiny Jennifer Renee from her mother's arms Thursday afternoon was an impostor, Arlington Hospital officials say. And neither the infant nor the "nurse" who said the baby needed a blood test has been seen since.

"I was sitting there with my baby on my lap and I was playing with her," the 23-year-old Capitol Heights mother said yesterday during a tearful hospital news conference with her husband Herbert, 36, at her side.

"The lady came in and she said, 'Mrs. Smith?' I said, 'Yes.' She said, 'We have to take the baby to the lab.' I got kind of scared. I said, 'What's wrong with her?' She said, 'Nothing, a routine blood analysis.' "

But Smith said she noticed that the "nurse" did not swaddle the baby in her pink and blue striped blanket the way most nurses do.

"She wrapped her kind of loose, picked her up in her arms and carried her out," Smith said, sobbing. "That was the last time I saw her."

Arlington County police spokesman Ken Rosenberg said yesterday that police had no clue or motive and had called in the FBI to help find the baby, for whom a search was conducted in the hospital and on its grounds.

Rosenberg said the baby's mother described the woman as in her mid-to-late-thirties, wearing blue hospital scrubs with a blue and green smock with butterflies on it. Smith's roommate described the woman as wearing a white lab coat over a white dress with yellow ruffles, Rosenberg said.

Hospital spokeswoman Debra Proud said the hospital has stepped up security, placing a guard on the maternity floor. She said hospital officials had no idea where the woman obtained the medical garb or how she may have left the hospital undetected by staff members.

"Unless you want to have a locked facility, you are going to have a free flow of people in and out of the hospital," Proud said. "We don't always know who the people are."

Herbert Smith said he was angry that a stranger could walk in posing as a hospital employe and take the baby. "Apparently, any baby can just walk out of here with anybody," he said. "It's just that simple."

He said he had no idea why Jennifer, the couple's fourth child, had apparently become the victim of a kidnaper.

"There is nobody really that hates us that much to take our child, as far as I know," he said. "It must have been handpicked. They came in here and asked for her by name.

"It's a terrible tragedy it did happen," he said. "I hope it wasn't black market, and I hope like hell we get her back."

Rosenberg said hospital personnel did not know that the baby was missing until a nurse asked Loreli Smith where the baby was Thursday afternoon.

Told that the baby was at a lab for blood tests, the nurse called and talked to a technician, who noticed tests being performed on another baby there and told the nurse that they were not finished, Rosenberg said.

Eventually, hospital personnel learned that the baby being tested was not Jennifer Smith, he said, and hospital officials called the police.

Loreli Smith said two nurses came into her room and asked her to walk down the hall with them. "I kept asking, 'Where is she?' They wouldn't answer me, just told me to step in the room, and then they shut the door and said they couldn't locate her," she said.

Police spent most of yesterday questioning the Smiths, family members and hospital staff members. Rosenberg said police had "no information to verify" rumors that the abduction paralleled one dramatized on a soap opera last week.

Rosenberg said the baby was in good health and was staying in the hospital while her mother recovered from the cesarean birth on Tuesday. Proud said Herbert Smith, an employe of a tire and auto shop, and his wife came from their Maryland home for delivery at Arlington Hospital because her obstetrician practices there.

The hospital, which recorded about 2,700 births last year, has been promoting the variety of birth services offered through its maternity program.

Just before Loreli Smith was wheeled back to her third-floor room after the brief news conference, she said, "I just want her home . . . . Bring her someplace where she'll be safe so I can have her back again. She's so little and so pretty."