A Fairfax judge ruled yesterday that the prosecution in the case of a Northern Virginia physician charged with performing an illegal abortion may use the term "unborn child" despite vigorous objections from the doctor's attorney.

The term was used repeatedly by chief Fairfax prosecutor Robert F. Horan Jr. at a pretrial hearing in Fairfax Circuit Court yesterday for Dr. Chris Simopolous, whose trial on a charge of performing the abortion on a 17-year-old girl is scheduled to begin today.

Horan "has no right . . . to try to convert an unviable fetus into an infant," argued defense attorney Roy Lucas. "Use of that word is medically improper . . . [and] potentially inflammatory" to jurors," he said.

Simopolous, 42, who has offices in Woodbridge and Falls Church, is charged with violating Virginia law that requires performing second-trimester abortions -- those done after the 13th week of pregnancy -- in a hospital. He is accused of performing an abortion on the 17-year-old at his Falls Church American Women's Clinic last November. The girl was five months pregnant at the time, according to the prosecution, and her dead fetus was later found in a wastebasket at a Springfield motel, where she went after the doctor injected her with a salt solution.

Horan, noting that the Virginia abortion statutes use "unborn child," argued that the law gives him a right to use that term rather than the word fetus.

"This is a child," Horan said. "It's not a giraffe. It's not a monkey, nor is it a goat."

Simopolous, he said, intended "to kill that unborn child."

Circuit Judge F. Bruce Bach said he will permit Horan to continue to refer to the fetus as an "unborn child." I certainly wouldn't require the prosecutor to refrain from using terms that the statute uses," Bach said.

At yesterday's hearing, Simopoulos' attorneys challenged the constitutionality of the Virginia abortion laws, saying they place an unnecessary hardship on minors and restrict their ability to get legal abortions. The judge said he will rule on that challenge today.

If convicted, Simopoulos could be sentenced to as long as 10 years in prison.