The Arlington School Board unanimously adopted new guidelines last night that will permit students who have contracted the AIDS virus to continue to attend the county's schools unless it is determined the student poses a health risk to others.

Under the old guidelines, a student testing positive for the AIDS virus would have been barred from attending classes until it had been determined that he or she posed no risk to others.

Under the new guidelines, a decision whether the student should be allowed to continue attending classes would be rendered by the school superintendent in consultation with the student's physician, family and health officials.

"So much has changed in the area of AIDS information that we felt we needed to change the guidelines," said Richard Blocker, director of student services for the county.

The change in policy also was in line with a mandate from the Virginia Board of Education.

There was little discussion and no public debate on the policy last night, and school system spokesman David Rorick said there have been no known cases of AIDS-infected students in the county's public schools.

In Arlington, as in Fairfax County, where there have been at least two reported cases of a student contracting AIDS, the policy calls for notifying parents that a child in the school system has tested positive for the virus without identifying him or her. State guidelines guarantee the confidentiality of students with AIDS.

Under the guidelines the Arlington School Board approved last night, parents of a child infected with AIDS are encouraged, but not required to report that fact to school officials, Rorick said.

Maryland and the District of Columbia have similar policies for handling AIDS cases in their schools.