Parents at Riverside Elementary School in Fairfax County learned yesterday through a letter sent home with their children that a kindergarten girl with AIDS will be returning to classes soon, more than a month after her widely publicized removal.

The 2 1/2-page letter, which told parents that health authorities believe the pupil's attendance "does not represent a significant risk to other students or staff at the school," invited them to a special PTA meeting tonight to discuss the decision to readmit her. A Red Cross pamphlet on AIDS was enclosed.

The girl, who is believed to have acquired AIDS from a blood transfusion shortly after birth, was removed from school in November. Her mother filed suit against the school system Dec. 22 seeking her child's return to school. After holding a news conference in which he questioned whether children with AIDS should attend public schools, Superintendent Robert R. Spillane followed the advice of county Health Director Richard K. Miller and agreed to readmit the child under regular medical supervision. The School Board endorsed that recommendation Saturday.

The letter that went home yesterday was met with surprise in the Riverside community, a potpourri of neighborhoods ranging from upper-middle-class houses to trailers, off Rte. 1 in the southeastern Mount Vernon section of the county.

"Most people I've talked to have been shocked because they didn't know, but they're concerned about the child," said Kathy Tank, the PTA secretary. "No one wants it to be a big stink like what happened in Florida and different places . . . . So far, there's been no hysteria."

Riverside is a well kept school of 450 pupils, five dozen of them in a program for low-income children, and its standardized test scores are well below the county average. It is officially a "special needs school," which means its population is more transient and minority than the county average.

School and health officials met yesterday with teachers at Riverside, including the girl's teacher and kindergarten aide, to explain the decision and answer questions.

No date has been set for the child's return, but school system spokeswoman Dolores Bohen said it would not be until parents were informed. The girl's name has not been made public.

Because the letter went home only yesterday, two days after the School Board voted to readmit the child, Riverside PTA officials said they had not heard from many parents but were trying to keep the emotional temperature down.

Tank said, "I'm not as concerned about the fact that there is an AIDS student going to our school as about the fact that people will overreact." Tank has three boys at the school, none in kindergarten.

PTA President William E. Herker, who has a daughter in the fifth grade and a daughter in the sixth grade at Riverside, said he was not worried. "I know there is a committee set up to monitor the child's progress and from all the information I can obtain right now, I can see no reason why either of my children would be endangered by going to school with this girl," he said.

But Herker said he expects some parents to be upset with the decision to let the child return: "I'm expecting my {answering} machine to go crazy tonight."

The letter to parents from Principal John Spataro said that an "exhaustive review of medical information" determined that the child did not pose a significant danger to others at the school. It cited guidelines from federal and state health authorities recommending that most children with AIDS be allowed to attend school.

AIDS is not transmitted by casual contact, sharing bathrooms, touching, or hugging, said the letter, which was read to a reporter by a parent. It noted that not one case of AIDS has been reported to have been transmitted in school or at a day care center. It also expressed hope that the situation could be handled in a "reasoned and compassionate way."

The pupil's medical condition will be closely monitored, the letter said. It noted that the School Board requested that a registered nurse be present at school while the child is attending.

In voting to readmit the child, the School Board also ordered that her condition be reviewed at least every week. A panel including a Health Department employe, pediatric infectious disease specialist and school system employe will review the child's condition at least every three months, and Spillane will be authorized to remove her if her condition worsens.

The School Board has ordered Spillane to draft a written policy on AIDS for discussion Thursday night.