The federal government has authorized tests on humans of a synthetic substance that appears to have a powerful inhibiting effect on the AIDS virus in laboratory experiments.

Called Peptide T, the substance is a synthetic copy of a naturally occurring messenger chemical that permits communication between the brain and nerve cells throughout the body.

Because Peptide T contains a pattern of amino acids similar to that of a piece of the AIDS virus, it appears able to block the virus from penetrating cell membrane.

Candace Pert, the neuroscientist at the National Institute of Mental Health (NIMH) who first developed the synthetic version of the substance and tested it against acquired immune deficiency syndrome, announced her test-tube findings last December.

The Food and Drug Administration withheld approval for tests on humans until her findings could be verified independently. Pert announced yesterday that Oncogen, a Seattle research firm, has verified the antiviral properties.

FDA approval for clinical trials came last week.

Only one drug, AZT, has been proven effective in prolonging lives of AIDS patients, but it often has severe side effects. Several other drugs are in various stages of testing. In early tests, Peptide T has shown no toxic side effects.

Peptide T was given to four AIDS patients in Sweden on a compassionate-use basis. The four were considered terminal.

Three were given the substance intravenously for one month, taken off it for three weeks and given it again for a week. They appear to be in remission, one returning to his job as a symphonic musician. The fourth died before completion of the course.

The Swedish team at the Karolinska Institute in Stockholm has also been approved for more extensive clinical trials, the NIMH scientists reported.

Pert presented her work on Peptide T at the Third International Conference on AIDS this week at the Washington Hilton.

In a subsequent briefing, Pert, NIMH Scientific Director Frederick K. Goodwin and Dr. Michael Ruff, a neuroscientist in Pert's laboratory, reported that, using Peptide T, they had produced antibodies that may prove effective as a vaccine against the AIDS virus.

Pert said she deduced that Peptide T might work after looking at computer printouts of related viruses active in the central nervous system, including the Epstein-Barr virus. All had amino-acid strings similar to each other and to Peptide T.

The peptide is very similar to a natural chemical messenger known as VIP, known to work in the brain and intestines. The AIDS virus may pierce membranes of immune-system cells by "pretending" to be VIP and being recognized by the cell receptor.