Would-be parents from Massachusetts have contracted with a Fairfax County woman to bear their child and are asking the Fairfax Circuit Court to answer an unusual question before the child is born: Who will be its legal parents?

The medical procedure used in this case, ovum implantation, is also unusual. If "Baby Doe," as the unborn infant is being called in court papers, is born in Fairfax as expected on Dec. 11, its birth would be what is believed to be only the third of its kind in the world.

"We're asking the court to determine the paternity and the maternity of the unborn child," said James R. Hart, a Fairfax attorney representing the Massachusetts couple. "It's arguably not clear." The issue is being raised in Fairfax because that is where the surrogate mother lives.

In typical surrogate cases, such as the celebrated "Baby M" custody dispute, the surrogate's egg is fertilized. But in ovum implantation, the infertile couple's ovum and sperm are joined in a laboratory, then the fertilized embyro is implanted in the uterus of the surrogate.

The surrogate "does not contribute to the pregnancy," said Dr. Wulf H. Utian, who, along with a team of other doctors at Mount Sinai Medical Center in Cleveland, pioneered the process. The surrogate, he said, is "acting as baby sitter for nine months."

Utian said there is no question that infertile couples who provide the fertilized embryo are the biological parents. However, he said, their legal claim to parenthood is more complicated to establish. "Society and the courts are grappling with what we can achieve medically," he said.

In the Fairfax case, as in a precedent-setting Michigan case, there is no argument between would-be parents and the surrogate. The Massachusetts couple, which is using the names John and Mary Doe to maintain privacy, is merely trying to reaffirm its contract with the surrogate by asking the court for a "declaratory judgment" on the question of who are the legal parents, according to Noel P. Keane, a Michigan attorney.

Keane said the legal presumption has always been that the woman who bears the child is the mother. In the typical surrogate case, a contract is drawn before conception and the would-be parents adopt the baby after its birth.

In ovum implantation cases, "these parents don't want to adopt their own child," Keane said. In addition, he said, they want answers to such questions as whose name will go on the birth certificate.

Keane, whose firm handled the legal affairs in the first ovum implantation birth in April 1986, said a Michigan judge issued an interim order before the child's birth declaring the infertile couple to be the legal parents.

The order became final after the child was born and a blood test was administered to validate the claim, Keane said. The name of the biological mother, not the "birthing mother," was placed on the birth certificate, he said.

Matthew L. Myers, a Washington lawyer who represents a Maryland group called Surrogate Motherhood Inc., said that the legal issues raised are "all uncharted waters."

Hart, the Massachusetts couple's attorney in Fairfax, said there are a host of questions not addressed in Virginia statutes: Who is legally obligated to support the child? Who does the baby inherit from? Who inherits from the baby?

Susan Hicks, attorney for the surrogate, said it is also unclear even whether the court would agree to rule on the issue before the birth. Her client, who is identified in court papers as Jane Roe, did not want to be interviewed.

According to Utian, who is director of the obstetrics department at Mount Sinai, Hicks' client will be only the third woman in the world to give birth to a child conceived through ovum implantation. He said the first was believed to be the baby born in Michigan and a second is believed to have been born in South Africa.