Helen Chambers brought her husband home from Springfield State Hospital near Sykesville, Md., four years ago Thanksgiving. Although only 68, he no longer recognized his wife. In the few short weeks of his hospitalization, Snowden Chambers had lost the ability to control his bodily functions.

From being the wife of a sick and profoundly disturbed man, Helen Chambers became the caretaker of an adult with all the characteristics of a very young child. Her husband was and is suffering from Alzheimer's disease, an irreversible, as yet untreatable deterioration of the brain that accounts for 50 percent of the incidents of senile dementia -- senility -- in the United States, according to medical experts.

The effect of the disease on Snowden Chambers is clear and easy to see. But he is not the only victim. In a very real sense, the disease that is destroying him is also consuming his wife.

Over the last 10 years her life has come to be dominated by her husband and his condition. Her story is becoming a familiar one as the population of the United States becomes older, increasing the prevalence of Alzheimer's disease and the social and financial catastrophes it can create.

At 60, Helen Chambers says she yearns for the warmth and comfort of a normal human relationship. The times she and her husband looked forward to sharing after their children were grown, the career she had embarked upon, the friendships the Chamberses had cherished--all shattered by her husband's disease. "My initial reaction," she says, "was, 'What a waste!' It is. It's a waste of two people--him and me."

Since her husband requires almost constant care, she can leave the house only when she can find someone willing and able to watch and take care of him. One adult son lives in a basement apartment in the house and helps when he can, but he has to be away much of the day. Her other two sons live elsewhere. She said she has made a special effort to shield her sons from the psychological strain that accompanies the disease.

Theoretically, Chambers could be in a nursing home, but his wife would have to pay out of pocket between $17,000 and $33,000 annually for such care, an expenditure that would deprive her of any resources to take care of herself in her own old age. He is eligible for Medicare, the federally supported health-insurance program for older persons, but Medicare does not cover extended stays in nursing homes. Medicaid, the federal-state health-care program for indigents does pay for nursing home care, but Helen Chambers would have to be virtually penniless before her husband would be eligible for Medicaid.

The occurrence of Alzheimer's disease is age-related. Although cases have been reported among people in their 40s and Alois Alzheimer reported the first case in 1906 involving a 51-year-old patient, it appears most frequently in persons 60 and older. An estimated 20 percent of persons 80 and older--the population segment with the fastest growth rate in the United States--suffer from Alzheimer's.

Alzheimer's does not leave its victims immobile. In its early stages, it attacks speech and memory but leaves motor functions intact. The victim often can move about freely. Along with restlessness, the disease is characterized by endless repetition of meaningless actions--opening and closing drawers--wandering from room to room, taking long walks, and incontinence in the later stages.

Since the mind no longer functions properly, the controls and judgment a normal healthy person has are missing. The Alzheimer's patient cannot be left alone. Unless drugged, he or she may spend the night roaming, pacing, keeping others in the household awake. Helen Chambers has put dead-bolt locks on all the doors so that her husband cannot open them and wander out of the house.

Her husband is a presence, but no longer a companion. It is as though his body had been taken over by some alien being, as in some Hollywood Grade B movie.

By the same token, she has become a stranger to him. "I have been as many as seven people at one time to him. According to my function and the room I was in, he had me separated into all these different people," she said. "He would warn me against the woman who had just given him a bath: 'She's a bitch. Watch out for her. Watch out for the old lady who's out in the hall. She's always watching.' He would warn me against me--the person he would perceive. He would warn me sometimes if I would kiss him, 'Watch out! My wife may find out.' "

Helen Chambers cannot quite decide in her own mind who the man is who is living in the room down the hall from hers. On the one hand, she speaks of him--and to him--with the love of a devoted wife. "There is still a bond," she explained. "I still love him. He doesn't know me . . . We had a very, very loving marriage. He was extremely fond of me, that's probably why I stay with him.

"He used to say, 'Well, one of these days you're going to look back and you're going to say, "God, that guy really loved me." ' He said, 'You don't realize it now, but you're going to look back and remember.' And I do."

On the other hand, she already appears to have dealt with her husband's death. "He had a room full of keys, trophies, citations, thank yous, you know, honorary citizenships to various places. It was like a shrine in there," she said. "I took it all down. People can't understand how I could do that. I just put them in a box. I couldn't stand to look at this, because some wives do this. They set up a shrine to what their husband used to be. I took the pictures down of him with Hubert Humphrey and him with Lyndon Johnson and him with Jack Kennedy. This isn't the same person that was friends of people in high places and worked on programs with them."

Occasionally, Chambers' behavior is utterly different from when he was healthy. He has struck his wife. "When he gets mad at me, he manhandles me. He pushes me around. He kicks," she said.

This behavior is confirmed by families of other Alzheimer's disease patients. The wife of another apparent Alzheimer's victim showed a visitor bruises on her body caused by her husband the previous night when he resisted her attempts to return him to bed. When asked to explain his behavior, the husband could not clearly recall the incident, which had occurred only hours before.

In this particular case, the wife estimated that she is able to sleep five consecutive hours a night only once in a month. The other nights, she said, she is awakened by her husband's ceaseless prowling.

Although physically and intellectually still energetic, Helen Chambers talks about her life as though the active part of it is over. "It isn't as if I have another, better life to look forward to," she said. "Four years ago, I thought I did. But now I realize I don't."

Physicians and medical researchers simply do not know what causes Alzheimer's. Four avenues are being investigated to determine if the disease is caused by a slow-acting virus; genetically; by excessive accumulation of aluminum or other toxins in the brain, or by changes in the brain's chemistry.

At the moment no method exists for certain diagnosis short of examining cells taken from the cerebral cortex, the communications center of the brain and the locus of the disease.

Because of the risk to the patient and lack of a treatment for the disease, an absolute diagnosis is usually made after the patient's death, by an autopsy. An autopsy will show a significant change in the brain, characterized by the presence of an abnormally high number of bodies known as neuritic or senile plaque and tangles.

While the patient is still alive, diagnosis is made by a process of elimination--ruling out other possible causes of the symptoms. According to Dr. Robert Katzman, chairman of the Albert Einstein Medical School's neurology department, the probability of correct diagnosis of Alzheimer's is 80 to 90 percent, using current methods.

Over the past 10 years, the understanding of senile dementia -- senility -- has increased significantly. Medical researchers now believe that senile dementia is not one condition, but 50 or more, not all permanent or irreversible. The widespread assumption that old age naturally brings a general and debilitating deterioration of the brain, accounting for senility, is not correct, according to medical experts. Nor is hardening of the arteries -- arteriosclerosis -- a direct cause of senility.

Senile dementia, medical scientists are finding out, is no more an inevitable or a normal condition of aging than cancer or heart disease. "Normal aging," according to a special report of the National Institute on Aging, "does not include gross intellectual impairment, confusion, depression, hallucinations, or delusions. Such symptoms are due to disease and indicate the need for diagnosis and treatment."

Roughly half of the cases of senile dementia in this country are of the Alzheimer's type. Another quarter can be accounted for by a series of small strokes, called multi-infarct dementia. Strokes are caused by the closing or clogging of a blood vessel bringing blood to the brain. Deprived of the oxygen the blood brings to the brain, tissue dies. Since nerve cells do not regenerate, a person who suffers enough strokes eventually will become demented--senile.

Another 20 percent of incidents of dementia are caused by depression, drugs or secondary effects of illness and are not permanent or irreversible. The causes of the remaining 5 percent are unaccounted for.

Since Alzheimer victims--like cancer victims--rarely die directly of the disease but from secondary conditions like heart or kidney failure or pneumonia, its true importance as a cause of death in the United States has been masked. Alzheimer's disease has been estimated to be the fourth or fifth leading cause of death in the United States today.

In 1980, roughly $22 billion was spent on nursing-home care in the United States. Dr. Robert Butler, director of the National Institute on Aging, estimates that half of the country's nursing-home patients are victims of Alzheimer's disease or some other form of senile dementia. By 1990, according to estimates of the Health Care Financing Administration, the nation's total nursing home bill will be more than $75 billion. Butler estimates that roughly $30 billion of this amount will be spent to institutionalize patients with Alzheimer's or the other forms of dementia.

Some limited research is proceeding. In fiscal 1981, the federal government allocated about $15 million and in fiscal 1982 about $17 million will be spent for research on Alzheimer's and related disorders. Butler called these amounts "minuscule," both in absolute terms and considering the potential financial savings if a cure or even a treatment could be found--as researchers say is possible before the end of the decade.

Despite the relatively low level of funding for research on Alzheimer's disease, medical researchers have made significant progress toward understanding the illness in the last 10 years. The brain plaque, it is now understood, consists of degenerating nerve terminals with a core of fibrous protein. Research also has shown changes in the brain's nerve cells themselves. In addition, research has found that the tangles, which are paired, interwoven spirals, represent a malformation in the cell body of the neuron--the heart of the body's nervous system.

According to Dr. Robert Terry of New York's Albert Einstein College of Medicine, who has done much of the significant research in this area, no clear cause-and-effect relationship between these malformations and Alzheimer's disease has yet been established. However, Terry said, "If you alter those very important things, it's impossible for me to believe that it doesn't have a functional effect."

In addition to Terry's research, Dr. Peter Davies, a biochemist, has found a high correlation between the breakdown of a particular enzyme in the brain--choline acetyltransferase--and the incidence of Alzheimer's disease and senile dementia of the Alzheimer's type.

Still unknown are the causes of this enzyme deficiency and the connection between it and the disease. Independently of Davies' work, however, a psychiatrist at the Bronx Veterans Administration Hospital, Dr. Kenneth Davis, found that the drug physostigmine enhanced the memory function of subjects to whom it was given in a controlled experiment.

Physostigmine inhibits the breakdown of a critical product of choline acetyltransferase, raising the possibility that some of the symptoms of Alzheimer's can be retarded or even reversed while scientists continue to seek a way of either preventing or curing the disease.

Terry summed up the situation: "We have a lot of clues in regard to the mechanism of the disease, and these are beginning to come together."

Butler, of the National Institute on Aging, finds a certain irony in the advances of modern medicine. "The triumph of this century in making it possible for people to live longer," he said, "makes even more poignant the fact that one of the fallouts of long life for some people is the vulnerability to this devastating disease.

"I want to say that in a qualified manner, because clearly if 4 or 6 percent develop the disease, then something like 95 percent don't have it. But in absolute numbers, or as a proportion, it's just astronomical, especially since numbers of older persons are growing daily in this country alone by 1,600 persons and 600,000 roughly a year.

"So that if we don't find some remedies, some forms of prevention, some effective ways of treatment of senile dementia of the Alzheimer's type, we're going to have an incredible burgeoning of the nursing-home population, enormous anguish in families, great and escalating costs and, I fear, the prospect of some cold-bloodedness."