In Prince William County, a student whose blood tested positive for exposure to AIDS quietly returned to class this month, with School Board permission. In Fairfax County, a few miles away, the school system was slapped with criticism and a lawsuit over the case of a kindergarten girl removed from class because she has AIDS.

The tale of how the two counties handled one of the hottest issues for public schools in recent years, some say, shows what a difference a written policy makes.

The Prince William County student -- identified only as a girl older than kindergarten age -- was allowed to attend school after a team that included school officials and the county health director evaluated the case and recommended her readmission to the superintendent. The girl had been out of school for six weeks, receiving tutoring at home. On Dec. 2, the School Board voted to let her return to class.

The sequence of events followed a prescribed procedure approved last January by the Prince William County School Board. Superintendent Edward L. Kelly said yesterday that administrators received only four calls from parents and staff members concerned about the case, and several School Board members said they received none.

"There has been no hue and cry at all," said board member Patricia L. Cusey. "Frankly, I expected more."

By contrast, Fairfax County was sued in federal court last week by the mother of a kindergarten girl removed from school last month because she has AIDS, and PTA officials criticized the school system's handling of the case. Both the girl's mother and the PTA officials complained about the county's lack of clear written guidelines on AIDS.

Superintendent Robert R. Spillane defended his actions at a news conference last Tuesday, and his off-the-cuff remark to reporters afterward questioning the lawsuit quickly erupted into a major controversy. Some School Board members also complained that the first they had heard of the case was when the mother filed suit in response to Spillane's actions.

"If the School Board had adopted a policy like we had asked them to, this never would have happened," said Kevin Bell, president of the county Council of PTAs, whose national guidelines favor the admission of most students with acquired immune deficiency syndrome, a fatal viral disease that attacks the body's immune system.

"Misunderstandings arise when there is a lack of direction," Bell said, adding that it was unfortunate the girl's mother had to "go to a lawyer to solve something the school system should have solved."

Lawyer Kenneth Labowitz, who represents the mother of the unidentified Fairfax County child, said one reason he filed suit was because school officials gave him a moving target by refusing to outline the procedures they used to consider evidence in the case.

School system spokeswoman Dolores Bohen disputed the contention that a policy was the crucial difference between Prince William and Fairfax. "Perhaps lawyers and the press are the difference," she said, referring to the lawsuit and to the subsequent news coverage. "I don't know that having a written policy would or would not have changed the lawsuit."

Spillane defended the school system's actions last week by saying that officials consider each situation individually, and that he was awaiting the advice of a review team and the county's health director before deciding what final action to recommend. A written policy, he said, would handcuff officials at a time when medical evidence about AIDS is changing rapidly. Spillane said it was unlikely he would favor the admission of a pupil with AIDS into a regular classroom.

On Saturday, the Fairfax County School Board reversed itself and ordered Spillane to draft a policy to be discussed Jan. 7, and adopted after public hearings. One reason for the reversal, board members said, was that Spillane's comments about the case were interpreted by some as evidence that he had made a judgment before all the facts were in.

The chairman of the Prince William County School Board, Gerard P. Cleary, said he was surprised to learn that Fairfax County had no written policy on AIDS -- and all the more so because "we've always looked at Fairfax as the most progressive school system. Ever since I came to the county in 1954, people have been saying, 'Why don't you copy Fairfax?' "

The Prince William County policy states that a student with AIDS will be excluded from school until a team of school officials and the county health director evaluates the child's behavior, neurological development, physical condition and expected interaction with teachers and other students.

The child, as well as his or her parents, guardians and physicians, may participate in the process, the policy states. A psychological evaluation of the child may be ordered.

"We want to be able to determine: Is that person capable of understanding his condition, understand his or her responsibilities to others?" Kelly said.

In the case recently decided, the committee met during a period of six weeks. Because the girl had been removed from school for related health reasons, "we were never faced with the necessity of having to suspend the child," Kelly said.

The health team recommended that the student's activities be limited in situations where she might get hurt and bleed, and if the student fights, she will be considered a health hazard and placed on home instruction.

Her case will be reevaluated in January and in May, officials said.

Arlington County's School Board adopted a similar AIDS policy in April 1986, providing that a team must review each case within five working days and report to the superintendent, who has 10 working days to decide on how the child will be taught. Alexandria's school system is developing an AIDS policy. Neither system has a known case of AIDS among students, officials said.

Labowitz said students who tested positive for exposure to the AIDS virus or who had the actual disease were enrolled in class without incident in at least two other Virginia school systems. He said one was in Waynesboro and would not identify the other, but said the student initially was refused admission.

In Waynesboro, "the community has been reasonably quiet and, I suppose, in that sense, supportive," Dr. Clifford Caplen, health director for the Central Shenandoah Health District, told The Associated Press.

Guidelines published by the state Health Department and the federal Centers for Disease Control in Atlanta recommend that most students with AIDS be admitted to class without restriction. Limitations should be considered only when the student is liable to bite, bleed or otherwise be unable to control bodily fluids, according to the guidelines.

At his news conference last Tuesday after the lawsuit was filed, Spillane cited state law barring pupils with contagious diseases from the classroom as the basis for removing the girl from kindergarten. He announced that a review team studying the case would make a recommendation to him whether she should return to school. School officials later amended his statement to say the team would pass information to county Health Director Richard K. Miller, who would make a recommendation to Spillane. The School Board must approve any expulsions.