Erecting gates around the Farragut West station to keep the homeless from sleeping in the station, while necessary, is but another Band-Aid applied to a severely hemorrhaging wound. Citizens do have the right to be able to use public transportation without having to step over personal debris, bodily wastes or sleeping bodies in stairwells. At the same time, citizens have an obligation to ask why the homeless are there.

One reason is a lack of shelter facilities and low-cost housing in the District. During the same week that Metro made its announcement I visited Emory School, which is being used as a women's shelter by the Community for Creative Non-Violence. On the evening I was there, 165 women occupied space planned for 80, and the shelter was forced to turn away additional women. Women were sleeping on cots in crowded hallways and even on the landings of stairwells. Classroom decorations from the school's earlier incarnation were still visible, a poignant reminder of a happier past, and at least one shelter resident had been a student in the same classroom in which she now slept.

A second reason why the homeless sleep in public places is that at least one-third of them are seriously mentally ill. For those living on streets, in parks and subway stations the percentage is considerably higher -- 62 percent according to one New York City study. Most such individuals in Washington were once patients in St. Elizabeths Hospital and state mental hospitals, released during the era of deinstitutionalization. In theory deinstitutionalization promised that psychiatric outpatient facilities would be available in the community to provide ongoing care for such individuals, but this was not the case. The District of Columbia has been rated in a national survey as having among the worst psychiatric outpatient facilities in the United States. As St. Elizabeths reduced its population from 7,300 in 1955 to 1,500 currently, most of the released patients received little or no aftercare. The process was one of depopulation, not deinstitutionalization; it was as if a policy of resettlement had been promised but only eviction took place. The homeless mentally ill on the streets are the visible reminder of these failed programs.

The third reason for homeless persons living in places like subways is the commitment laws of the District, which make it exceedingly difficult to rehospitalize and treat obviously mentally ill individuals until they are deemed to be dangerous. These laws were changed by well-meaning lawyers a decade ago, before it was clearly established, as it now is, that serious mental illnesses are brain diseases that can often be successfully treated with medications. Since the organ affected by these diseases is the same organ we use to think about ourselves, it is not surprising that many mentally ill individuals do not recognize their own need for treatment. And despite overwhelming evidence that living in the community without treatment is a disaster for many mentally ill individuals, groups like the Mental Health Law Project continue to petition the court to release from mental hospitals an ever-increasing number of patients. Such lawyers are like a solicitor sorcerer's apprentice, acting on behalf of their own ideals and not their clients' needs. As summarized by Dr. Loren Roth: ''A large number of patients have been kidnapped by a small number of lawyers in order to make a philosophical point on their own behalf.''

So, yes, shut the gates to the Metro station. There will be more gates to shut, and more again, and still more again until we address the underlying issues -- the lack of public shelters and low-income housing, the poor-quality psychiatric outpatient services and the laws governing involuntary treatment of the mentally ill in the District of Columbia.

-- E. Fuller Torrey is a research psychiatrist.