When a major government study suggested last week that one in five American adults suffers from mental illness, it also reported an equally astonishing statistic: only 19 percent of people with psychological problems seek help.

"Even those who do receive treatment are more likely to see a general physician than a psychiatrist or other mental health specialist," says Dr. Darrel A. Regier, who headed the National Institute of Mental Health's landmark study.

Researchers are eager to pinpoint why so few people seek help. Preliminary findings suggest two major stumbling blocks. One is the stigma of having a mental illness. "People really don't understand that getting help is a sign of strength, not a sign of weakness," says Stephen Goldston, Director, NIMH Office of Prevention.

The other is that medical doctors are able to diagnose correctly only about half of the patients who come to them with symptoms of psychiatric disorders, according to NIMH studies. "Many primary care physicians are not yet well skilled in diagnosing and treating emotional disturbance problems and mental illness," says Dr. Larry Silver, Acting Director, NIMH.

Two new NIMH educational campaigns could help. One, Silver says, will teach medical students and physicians how better to recognize the signs and symptoms of emotional disturbance and mental illness. The second campaign is designed to heighten public awareness of symptoms and to encourage treatment -- similar to efforts combatting cancer and heart disease.

Lack of money is another major reason why people with problems don't seek help. Insurance coverage for mental disorders lags behind that for physical ailments, although 26 states, including Maryland and Virginia, have passed mental health benefit laws. In the District, a bill requiring mental health coverage remains in committee.

But even those who have insurance coverage sometimes fear the repercussions of using it. The parents of one pre-med student at Howard University opted to pay for their son's treatment at another hospital rather than have him treated at the university. They were afraid that the same doctors who treated their son might later deny him entrance to Howard's medical school. "This is the kind of thing that happens," says Dr. James Collins, chairman of Howard's psychiatry department, "even when money and treatment are available."

Discrimination does occur at times against people who are open about their treatment. A woman who works for a local company with Defense Department contracts was denied a security clearance recently because she is seeing a psychologist. Her company's security chief declared that any employe undergoing psychological or psychiatric treatment would not be eligible for security clearance, regardless of the reason for therapy, said the woman's psychologist, who requests anonymity.

Other employers, however, are more open to mental health treatment. The World Bank, the Secret Service and the Central Intelligence Agency are just some of the organizations that offer employe assistance programs. "We offer counselling to our employes and their dependents as a benefit to them and to the agency," says CIA spokeswoman Kathy Pherson."Obviously employes can have all sorts of job and family problems and we try to deal with them as time permits."

But even without problems of stigma, diagnosis and payment, there are not enough mental health professionals available to treat everyone who needs help. "The real key," says NIMH's Goldston, "is not simply treatment and greater accessibility. The answer is prevention.

"Sources: Cost need not be a stumbling block to mental health treatment in the Washington area. Numerous services are offered on the ability to pay. Among the resources for referral and/or treatment:

Clergy. American Association of Pastoral Counselors, 385-6967; D.C. Pastoral Counselling Service, 332-2131; Pastoral Counselling and Consultation Centers of Greater Washington, 281-1870.

Community Mental Health Centers. D.C.: Geriatrics, 461 H St., N.W., 727-0438. Va.: Fairfax-Falls Church, 301 Maple Ave., West, Vienna, (703) 281-6420; Arlington County, 1725 N. George Mason Dr., 558-2815; Alexandria, 206 N. Washington St., 836-5751.

Directories. "The Referral Book," free from the Mental Health Services Administration, Room 821, 1875 Conn. Ave. N.W., 673-6692; "Directory of Mental Health Resources in Northern Virginia," $5 plus $1.25 postage, 536-4100.

Mental Health Associations. D.C.: 462-1122; No. Va.: 536-4100; Prince Georges County: 577-3140.

Psychiatric Referrals. D.C. and Va.: 682-6270; Montgomery County: 963-3100.

Psychoanalytic Society. D.C.: 338-5453 or 337-1617. Psychological Associations. D.C.: 543-3930; Md.: 596-3999 and (301) 992-4258; Va.: (703) 667-5544.

Social Workers Association. D.C., Md. and Va.: 347-9893.