Betty Malone wasn't convinced by the letter informing her that an AIDS-infected kindergartener's expected return to Riverside Elementary School poses no significant danger to others.

After reading the opinion sent home with about 450 Riverside pupils, the mother of two consulted a physician, who told her what she already knew: the AIDS virus is transmitted through bodily fluids.

But the worries remained. What if the infected child leaves a drop of blood on a water fountain and others drink from it? Malone wondered. Could she be assured that her children would not come in contact with the child's blood?

Malone reached a tentative decision.

When the girl with the AIDS virus returns to Riverside, Malone said, she will try to transfer her own kindergartener and second grader to another school. Yesterday, she kept her son and daughter home from the Fairfax County school because, she said, "I was afraid that the child would be there."

"We don't know what we're dealing with. They don't know all the answers about AIDS yet," she explained.

At a special PTA meeting last night, county school and health officials told parents the infected child is taking the new drug AZT, and that makes it unlikely she could pass the disease to others.

"This child is not infectious or contagious," said Area I Superintendent Jay D. Jacobs, adding that the child might be in school by the end of the week.

Jacobs said the school system will take "every precaution," including twice-weekly medical evaluations of the child to ensure that she would be removed from school if other children became endangered.

Malone said she was not reassured. "If you can't guarantee {our children's} protection," she told Jacobs, the infected child "doesn't belong in our school . . . . I don't want to risk losing my children through AIDS."

"I can give you as much guarantee of that as I can that your youngster won't walk out that door and walk in front of a school bus," Jacobs replied.

Both statements were applauded by some of the 300 people who had crowded into the school's cafeteria, indicating divisions over the School Board's decision to readmit the child to the school.

For many parents, it was difficult to absorb the knowledge that the child with AIDS who won permission to return to school after a highly publicized forced absence is a student at their children's school. While some accepted official assurances that the child presents no threat, others voiced a variety of doubts, and a few said they are unwilling to take any chances with their children's safety.

Parents interviewed yesterday unanimously defended the girl's right to a public education and sympathized with her plight, and those who questioned the wisdom of allowing her to mix with other children did so with none of the venom that has marked similar debates elsewhere.

Still, many of the more than two dozen speakers at last night's meeting used the forum to vent fears about the welfare of their children and as a platform to criticize the school system and Superintendent Robert R. Spillane for not having an AIDS policy and for not notifying parents of the case earlier.

Many offered their sympathies to the child and her family, and Tom Rodriguez, whose son is a fourth grader at the school, received loud applause when he said, "As a parent I want to make it clear our family welcomes this child back."

Others said they remain concerned that so much is unknown about the deadly disease and Malone said she is contemplating suing the school system to bar the girl's return.

The presence of AIDS-infected children in public schools has generated some bitter confrontations across the country. In Arcadia, Fla., the family of three hemophiliacs known to have been exposed to the AIDS virus received bomb and death threats. They moved after their house burned in a suspicious fire last August.

Earlier, school officials reiterated that the decision to allow the girl to return followed a thorough review of the case by medical experts.

Still, the questions multiplied.

"I have to get an education on which to base a sound decision," said Bernie deGastyne before last night's meeting. DeGastyne, who expressed the feelings of many Riverside parents, said he favors keeping his daughter in school, but his wife, Diana, feels differently.

"My kid's terrified to go to school," Diana deGastyne said. "Right now she's scared to death of everybody.

"I realize a 5-year-old's not going to have sex or use intravenous drugs," she said, "but at the same time . . . if a child gets into a fight, who's to say they won't bite?"

Diana deGastyne said she was considering moving or finding a full-time baby sitter for her daughter in another district, making her eligible to attend school there.

Ronald Johnson, a medical laboratory technician who drove his child to school yesterday, said other parents' fears are apparently fed by ignorance or misinformation about AIDS. "This particular disease is not a disease that is spread by casual contact," Johnson said. He said his greatest concern is the paranoia that could grip the school if the victim's identity is kept confidential.

"The kids'll be looking at each other wondering who's got it. I'm not sure that creates a healthy environment."

Stanley Barker, a father who criticized the decision to readmit the child, said the information he has received about AIDS has not allayed his fear. "If need be, we will keep our children home as long as they keep that child in the school," he said. "There's bound to be some kind of contact."

Barker said he would be satisfied if the school provided a separate classroom and bathroom for the girl. Already, Barker said, his sons in kindergarten and fourth grade avoid using the school bathrooms, fearing that the disease could be caught from a toilet seat.

When the child returns to class, she will be accompanied by a registered nurse provided by the county health department, said Dolores Bohen, a spokeswoman for the schools.