A young woman believed to be the mother of an infant who was abandoned in a Fairfax County apartment last month has telephoned police on two occasions, but hung up before investigators could ascertain her whereabouts.

Fairfax Investigator William A. Mullins said yesterday the woman, believed to be between 16 and 20, telephoned him about midnight on Sept. 12 after a television news report on the baby's discovery. The woman, identifying herself only as Sandra, called again a day later, but has not been heard from since, Mullins said.

"It's been nerve-racking. I think they were local calls. I tried to keep her on the telephone, but she was very hysterical and crying a lot and saying that she wanted her baby back," Mullins said. "Both conversations lasted no more than one or two minutes. She was afraid she might give herself away."

The child was found in the hallway of the Timberlane Park Apartments at 7352 Lee Hwy.

Preston Hendrick, a supervisor for Fairfax County's Foster Care Adoption Unit, which is caring for the child, said yesterday she was unaware that police might have been in contact with the infant's mother. "The Department of Social Services would be more than willing to work with the mother around planning for the raising of her child," she said.

"He's a precious baby, just as sweet as he can be. He even sleeps all night," Hendrick said of the baby, named Kenneth by department employes. She described Kenneth as well-developed and healthy, with brown eyes and light brown hair. Three children found the infant -- only two hours old at the time -- wrapped in sheets near the doorway of the third-floor apartment of one of the children, police said.

More than 100 callers have deluged Hendrick's office with offers to adopt the child, but Kenneth is ineligible for adoption until a six-month period has passed and all efforts to find the parents have failed, Hendrick said. "Every abandoned child brings a lump to their throats. People have been wonderfully generous in their offers," she added.

The child is currently living in a temporary foster home. Meanwhile, Mullins said he has checked area hospitals and a number of tips about the mother, but "we've come up with nothing."

"I hope they find her," Hendrick said. "He's just a poor little waif."