AIDS is a terrible diseasepainful, debilitating and, so far, invariably fatal. It is also contagious. As it spreads, urgent questions arise about controlling it.

It is a venereal disease. Your views about preventive measures are very likely to be related to your views about promiscuity, and particularly homosexual promiscuity. Although AIDS can be spread by heterosexual intercourse, homosexual contact remains the route by which it most commonly travels.

The implacable character of the disease gives an edge of real fear to the debate over the controls that society could impose. In California the November ballot will carry an initiative that would prohibit AIDS victims from working in schools or restaurants. It would also give health officials the authority to put them in quarantine.

Voters in California, and perhaps other places, are going to have to decide whether that kind of restriction would help. The answer begins with the research that epidemiologists have done over the past five years on the transmission of AIDS.

The federal Centers for Disease Control are carrying out the broadest of the collections of data. In addition to sexual contact, AIDS can be transmitted by blood transfer -- as in a transfusion, or injection with an infected needle -- and by birth to an infected mother. More than 22,600 cases of AIDS have been diagnosed so far in this country, and 95 percent of them can be shown to have been contracted by one of those three routes. The other five percent? Some were people who died before their doctors determined the means of infection. Some were small children who probably, but not provably, got the disease from transfusions. Perhaps beyond that there are some question marks.

The statistics are reassuring, but perhaps not quite reassuring enough. It's conceivable that, one day, a case showing some other path of transmission will appear. There's no way to prove that there's no other possibility. But the most reliable evidence of the virus' path is in the studies of those people who got the disease -- and those who did not.

Dr. Gerald H. Friedland and his colleagues at Montefiore Medical Center in the Bronx have been conducting a careful surveillance of people who lived at very close quarters with people carrying AIDS, but were not sexual partners. All of these people lived for at least three months, and some for years, with AIDS patients, most of them addicts, during the time when they were infectious. Dr. Friedland reported at the Paris meeting on AIDS last month that his team has found 145 people willing to cooperate, answering long lists of questions and undergoing painstaking and sometimes repeated medical exams. Although they are not further identified in Dr. Friedland's papers, most are obviously the families of the patients.

Nearly all of these people shared bathrooms and kitchens with AIDS patients. Most washed their dishes. Most hugged them. Some helped them bathe and eat. Many shared drinking glasses and plates. Seven shared toothbrushes with them.

Out of the 145, only one tests positive for the AIDS virus. She is the daughter, five years old at the time of screening, of two addicts, both infected. She apparently contracted the disease at birth from her mother.

Another kind of close-range study follows the people -- doctors, nurses, orderlies -- working in hospitals with many AIDS patients. Dr. Merle A. Sande reported last February in the New England Journal of Medicine that at his hospital, San Francisco General, more than 300 health care workers "with intense and sustained exposure to patients with AIDS for nearly four years" have been examined. All test negative for AIDS with the exception of 14 who are homosexuals. Dr. Sande said last week that, in the five months since February, that pattern has not changed.

There are only two known cases in which hospital workers have been infected -- both nurses, one in Britain and one in this country. Both were accidentally jabbed with infected needles -- and not only jabbed, but actually injected with infected blood in the syringe.

In one deeply poignant case, a mother acquired the disease from a child who had got it through transfusion. The mother cared for the child herself with great devotion and refused to wear gloves although the therapy required intravenous needles and the child was suffering from a bloody diarrhea. It seems probable that the mother was infected by direct bloodstream contact through nicks or small sores on her hands.

All of these studies come to the same point: there are only three known ways to get AIDS -- sexual contact, blood and birth. That is why the Public Health Service has concluded that there is no known risk of infection through normal daily contact at school or at work.

The Justice Department's famous memorandum last month did a real disservice by suggesting the opposite. The purpose of the memorandum was to argue that people carrying AIDS are not protected by federal law against discrimination, but it went well beyond that point to imply large and unknown dangers. After quoting the PHS's finding that there's no known risk of infection in the work place, the Justice Department went on to say: "It has been suggested, however, that conclusions of this character are too sweeping." In support it cited a quotation from a Harvard scientist, Dr. William Haseltine, in The New York Times.

Haseltine said, when I asked him, that the quotation misrepresents his view. He had been speaking at a forum about which the Harvard Crimson ran a story. A Harvard law professor, Alan Dershowitz, picked up the quotation from the Crimson in a piece that he wrote for The Times last March. On reading it, Haseltine protested to Dershowitz, who wrote a letter to The Times -- published in April -- clarifying Haseltine's position. The Justice Department memorandum, appearing in June, noted the original quotation but not Dershowitz's letter. Haseltine says that his own view of AIDS transmission is similar to that of the PHS.

Society has broad powers to impose sanctions -- Draconian sanctions, if necessary -- on the carriers of dangerous diseases. But those sanctions have to be justified by a real risk of contagion -- not merely an irrational fear of it, but a demonstrable risk. To bar AIDS carriers from employment in schools or restaurants or offices requires that, out of the cases now being reported at a rate of a thousand a month, there is at least one that was clearly contracted through the normal contacts of daily life. So far nobody has found that one case.

The writer is a member of the editorial page staff.