A serious chemical defect in the brain may result in suicidal tendencies, according to independent studies at three research centers.

The discovery bolsters a growing body of evidence that much aberrant behavior and mental illness is, at least in part, a result of biochemical problems, and could lead to a screening test to detect potential suicide victims and to a chemical treatment to correct the defect.

Scientists at the National Institute of Mental Health in Bethesda, Stockholm's famed Karolinska Institute and Wayne State University in Detroit have found deficiencies in the way the brain uses serotonin--a chemical carrier of nerve impulses between brain cells--in persons who have committed suicide or showed suicidal tendencies.

Serotonin is one of a small group of neurotransmitters, substances that maintain chemical conduction between brain and nerve cells.

Studies in recent years have strongly suggested that abnormal neurotransmitter activity plays a role in serious, pathological depression.The latest studies support that finding, although scientists caution that the theory will require further confirmation. However, NIMH is already trying a possible new drug treatment to correct the serotonin defect.

The new work has also found similar abnormalities and suicidal tendencies among victims of mental disorders and abnormal behaviors other than depression. Low serotonin activity, the research suggests, seems as common in highly aggressive and impulsive persons as in the pathologically depressed.

"This is very important," said Wayne State's Dr. Michael Stanley, noting that "the biochemical threat"--the common factor that may determine suicidal tendencies--may be present whether a person suffers from depression, personality disorder, schizophrenia or alcoholism.

Dr. Frederick Goodwin, director of intramural research at NIMH, said suicide may be the result of an interaction of depression and serotonin activity with traits like impulsiveness and aggressiveness.

The findings do not mean that all persons with this abnormal biochemistry may be suicidal, or that all suicide victims have abnormal biochemistry. Severe depression remains the most common cause of suicide.

But Goodwin said, "we can hope now that more selective drugs" to combat suicidal tendencies will soon be available.

The first link in the present chain of evidence was discovered in the past few years at the Karolinska Institute and NIMH.

Scientists reported that levels of the chemical 5-HIAA--a metabolite or product of serotonin--were abnormally low in persons who had attempted suicide, compared with normal persons and non-suicidal victims of depression. The Swedish institute found that, of persons who had attempted suicide and were found to have low 5-HIAA levels, 22 percent committed suicide in the first year after testing.

Stanley told the American Psychiatric Association last month of comparing the brains of nine suicide victims with nine normal brains. He measured the "binding sites" for the chemical imipramine: an anti-depressant drug whose binding measures the brain's ability to use serotonin. He found 44 percent of the normal number of such sites in the suicide victims' brains.

In similar research, Drs. Steven Paul, Joel Kleinman and Goodwin of NIMH found 30 to 40 percent fewer binding sites in the brains of 10 suicide victims, compared with normal brains.