A bitter tug-of-war begins here Thursday between the families caught up in the switching of two babies at the University of Virginia Medical Center, with both sides prepared to accuse each other of being unfit to raise one of the girls, Rebecca Grace Chittum.

The closed-door hearing in a tiny, rural courtroom will determine whether Rebecca, now 4, stays with the extended family she knows as her grandparents or is handed over to Paula Johnson, the woman who gave birth to her in the summer of 1995 and who is now suing for custody.

The fight comes in a case marked by repeat calamity, including the still unexplained infant switch at the hospital and the deaths in a car crash of the young couple who brought Rebecca home from the maternity ward. It also reflects the complete breakdown of earlier attempts by both sides to cooperate in raising the children, in the hope of avoiding a confrontation such as the one scheduled to start.

More than 30 witnesses have been subpoenaed to testify at the three-day hearing. Legal investigators for both sides have been digging through court records to find damning evidence. Lawyers already are preparing for almost certain appeals that could go as far as the U.S. Supreme Court.

Everyone involved is vowing to prevail.

"To just say, 'Go with that stranger,' could be devastating," said Michael Groot, the lawyer representing one set of the grandparents who have been raising Rebecca here. "We're going to retain custody in Buena Vista with these grandparents."

Responds Johnson: "I can't just go in there and jerk the child out of this house. But I missed three years of that child's life. I just want to be a part of this child's life."

Legal experts and psychologists said the fight for custody of Rebecca--and the possibility of a similar struggle in the future over the other switched girl, Callie Marie Conley, who uses Johnson's former boyfriend's surname--is likely to rival the most gut-wrenching of high-profile family disputes.

Richard Wexler, Washington director of the National Coalition for Child Protection Reform, urged the adults in Rebecca's life to reconsider waging a war over her custody and instead submit to mediation where a compromise can be worked out.

"It's extremely sad that all of these people seem more intent on carving up these children than finding some way to give them the love and security that they desperately need," Wexler said. "The only hope is one last-ditch attempt for everybody to start over."

That is unlikely to happen, according to people connected to both sides of the case.

Johnson has a team of lawyers handling a raft of lawsuits stemming from the baby switch, including a $31 million suit against the University of Virginia hospital. Rebecca's grandparents have accepted a $2 million settlement from the state, but Johnson has rejected a similar offer for Callie, calling the amount insufficient.

Meanwhile, she has already begun preparing her Stafford County home for Rebecca's arrival.

A new leaf has been inserted into her dining room table to make room for an extra chair at dinner time. Callie's room is being readied to share with Rebecca. And presents for Rebecca's birthday last summer sit waiting to be unwrapped when Rebecca "comes home," as Johnson puts it.

Lawyers for the Buena Vista grandparents say those preparations are premature. They vow to keep Rebecca in her home town and are expected to accuse Johnson of being an unfit mother by introducing evidence of a temper and of a criminal record involving an altercation between Johnson and another woman.

Johnson's attorneys are likely to attack the current arrangements for Rebecca's custody, worked out in a Buena Vista courtroom in December. In that hearing, a judge ruled that the child would spend three days of every week with one set of grandparents and four days with the other set. Because one pair of grandparents has divorced, Rebecca divides part of her time between her grandmother and her grandfather and his new wife.

"I have never seen a custody case where five people have custody of one child," said Johnson attorney Kenneth Mergenthal. "She's been going from one household to another. This can't be a good arrangement for the child."

Attorneys for both sides said the case could come down to the judge's interpretation of a section of Virginia law that allows children to be separated from their biological parents in "special circumstances."

John B. Curry II, a judge in the Waynesboro Juvenile and Domestic Relations Court who also has responsibilities in Staunton and Buena Vista, will have to decide whether the baby switch meets that test.

Michael Shapiro, a professor at the Columbia School of Journalism and the author of a book called "Solomon's Sword," said the legal process is inadequate to deal with a situation that is eerily reminiscent of the biblical tale about the struggle between two women over one baby.

"What all the grown-ups share is a dream for this child with themselves at the center of it and the inability to step back from these selfish desires," Shapiro said. "It shouldn't be about who's going to get this child. And yet it is, because the law is essentially an adversarial thing."

CAPTION: Paula Johnson talks to reporters in Charlottesville in November 1998.