LOS ANGELES (AP) _ AIDS impairs mental performance only in people who also display other symptoms, suggesting those who are infected with the AIDS virus but otherwise healthy can hold jobs involving public safety, scientists said Thursday.

The research is significant because it indicates that testing people for the AIDS virus can't predict whether the virus already has damaged their mental abilities, said Dr. Barbara Visscher, a co-author of the study and an epidemiologist at the University of California, Los Angeles.

The results, released Thursday, were published in February's issue of the journal Neurology. The findings are part of a larger study of AIDS conducted by researchers at UCLA, Johns Hopkins University in Baltimore, Northwestern University in Chicago and the University of Pittsburgh.

People who are infected by the AIDS virus - human immunodeficiency virus, or HIV - normally take several years before they develop symptoms and are diagnosed as having acquired immune deficiency syndrome.

''The findings suggest that people who are infected with the HIV virus, but have no symptoms of AIDS, are perfectly capable of holding down jobs demanding cognitive (mental) performance and may assume responsibility for public safety,'' the university said in a summmary of the research.

The new study involved 1,580 homosexual and bisexual men who were tested from 1986 through 1988 for speed of motor skills, attention and concentration, memory, manual dexterity and language skills.

The men were divided into four groups: 769 men who weren't infected, 620 who were infected but had no symptoms, 107 who became infected during the course of the study but lacked symptoms, and 84 diagnosed with AIDS symptoms.

The men with AIDS were most likely to fail the various tests, including those that measured manual dexterity and rapid problem solving requiring a physical response. But the researchers found no difference between the men who weren't infected and those who were infected but hadn't developed AIDS symptoms.

Many AIDS patients suffer dementia, or a loss of intellectual skill, and other signs of nervous system impairment during the final stages of the deadly disease, but there was little previous evidence on when such changes started.

''This is the first time we have been able to document continuing normal cognitive (mental) function over a long period with a very large group of HIV- infected subjects,'' said Dr. Eric Miller, director of the study at UCLA.