The National Institute of Mental Health has begun a unique diagnostic service for psychiatrists which, research scientists hope, will help limn some of the biological underpinnings of depression. At the same time, the tests could help the practicing psychiatrist better tailor specific treatments to the needs of patients.

With the (literally) mind-boggling neuro-biological breakthroughs of the past decade, psychobiologists are learning that some behavioral ills once thought to be centered in the disembodied sphere of the mind are a matter of chemistry. It is a concept at once more mundane and yet infinitely more complicated than traditional approaches to psychology and behavior.

Several tests have been developed at NIMH and elsewhere that suggest that some depressions may be linked to certain imbalances of the brain's electrochemical neurotransmitters -- the chemical substances that carry electrical information between cells -- or by other physiological abnormalities, malfunctions or dysfunctions.

Indeed, some of these tests already are being administered in some private psychiatric hospitals and institutes, but they require such sophisticated equipment and analysis that they are still either unavailable or financially out of reach to most. Moreover, as in any burgeoning field of scientific endeavor, the NIMH researchers are finding that the more they know, the more they have to discover.

As a result, NIMH psychobiological researchers -- mostly psychiatrists -- are offering to perform these new and elaborate examinations and workups on psychiatrist-referred patients suffering severe depressions.

According to Dr. David Pickar, of the NIMH Clinical Neuroscience Branch, patients will be brought into the clinical center for up to three weeks. Their psychiatrists will be given test results and will resume primary care when the tests are completed.

Pickar and his team would like to see how precisely the tests can distinguish between various kinds of depressions, whether they can pick out persons predisposed genetically to depressions and if they can serve as useful predictors of the treatment likely to be most effective.

For example, says Pickar, data from studies around the world suggest that there is an increased risk of suicide or suicide attempts among depressed patients who seem to lack a particular break-down product, or metabolite, of the neurotransmitter, serotonin, in their spinal fluid. "Naturally," he says, "we'd like to get a handle on that."

The researchers also want to find out how specifically the tests identify depression, as such, rather than some other disorder of which depression may be a part.

"Most research investigators tend to look at the depressed population versus the 'normals,' " says Pickar. "We want to look at the same tests in schizophrenic patients, for example, under the same conditions. The tests may show that there is an abnormality, but one that is not necessarily unique to depression. That's the kind of question we need to answer."

Psychiatrists with severely depressed patients who might benefit from the tests may phone project associate Dr. Alec Roy, 496-4303.

Unemployment is even worse than you think.

In an article in the current issue of the American Psychologist, Massachusetts psychologist Ramsey Liem and sociologist Paula Rayman have found that:

* Unemployed individuals suffered more episodes of high blood pressure, alcoholism, increased smoking, insomnia, nervous exhaustion and worry and anxiety.

* Families had more anxiety, depression, phobias.

The results, while not surprising, had not been measured so explicitly before. The authors suggest that in view of "the rippling effect" of unemployment in the community, it is a mistake to see it as only an economic phenomenon.

(On the day the report was issued, a middle-aged man walked into a Midwest newspaper office and stabbed himself -- not fatally -- after telling reporters he could not find work or pay medical bills.)

If all that hasn't depressed you too much, here's a quick test devised by an insurance company to give you a hint about how long you can live.

Called "The Longevity Game," the free booklet is designed to call attention to life-style changes that can add years to your life: like exercising more, smoking less, eating right.

For your free copy write: Northwestern Mutual Life Insurance Co., 720 E. Wisconsin Ave., Milwaukee, Wis. 53202.

More on drugs: The current issue of Ladies' Home Journal contains an excellent article called "Drugs and Driving," which is actually about medicines and driving.

A survey cited by the Journal says that 273 kinds of legitimately prescribed and over-the-counter medicines were involved in a survey of 10,000 routine drunk-driving arrests in which one out of four involved medicine, rather than alcohol. It talks about anti-histamines, cough medicines, eye drops and pain and mood medication, among others.

The article, however, does not remind those taking tranquilizers and sleeping pills that the effects can last many hours after ingestion. People forget that a cocktail on Wednesday evening can mix dangerously with the Dalmane from the night before. Still, the article is a good reminder, and includes a list of medicines that could cause you trouble behind the wheel.