AGED couple is having a leisurely Sunday breakfast in a d iner when, suddenly, the man explodes in a torrent of obscenities. L eaning across the table, his wife sings softly into his ear, ' 'Happy birthday to you, happy birthday to you.'' The man falls s ilent.
Another woman bends over a bed to straighten her husband's socks. It has taken an hour to bathe and dress him and she is exhausted. She has forgotten that he likes to have the cuffs of his socks turned in a certain way. Enraged, he lashes out with his working arm, striking her. She begins to sob.
A man sits on a couch beside his wife. ''Our children's names are Stephen and Alan,'' he recites. ''Our children's names are Stephen and Alan.'' The woman stares across the room. He holds a photograph to her face. ''Look, Stephen! Alan!''
In each of these cases, one partner has suffered a stroke, a form of cardiovascular disease affecting the blood vessels that supply oxygen and nutrients to the brain. While much has been written about physical changes in stroke, it is only in recent years that information on possible behavorial and emotional changes - and help in coping with them - has been available to victims and their families through so-called stroke clubs.
The couples described are among 200 families in a club sponsored by Brooklyn College and run by professionals at its speech and hearing center. The club, known as Focus (Families Organized for Community Understanding of Stroke), offers a range of social, educational and rehabilitative programs, including a monthly self-help and support group. There, family members - mostly wives, but also husbands and children - discuss feelings about stroke and strategies for dealing with it.
''Stroke is a crisis that hits the entire family,'' says Dr. Gail Gurland, a speech pathologist and the program's clinical and research director. She and Sam Chwat, its executive director, have done studies on the impact of stroke on family members. Initial feelings of guilt, hostility and depression are common, they say, coupled with fears that another stroke may occur.
In some ways, a stroke in the family is like any other medical crisis. Spouses frequently reverse roles -with wives of victims becoming the main breadwinners and husbands of victims taking over household duties. Children are called upon to manage parents' lives. There are the usual money worries and the usual problems of adjusting, at least temporarily, to restricted social and sexual activity.
''One thing that differentiates stroke from other devastating illness is that it is so abrupt and that it sometimes occurs relatively early in life,'' said Mr. Chwat, noting that an increasing number of the club's stroke victims are in their 30's, 40's and 50's.
Another aspect is the communication problem. Roughly half the victims lose all or part of their linguistic facility, at least for a time. They may be unable to form intelligible words or sentences, to understand spoken or written language or to name objects.
Rehabilitation programs help many to regain these facilities either fully or nearly so. Others experience continued speech and language difficulties, however, sometimes communicating by gestures, nonsense sounds or even curses.
In the stroke club, spouses learn that cursing or ''automatic language'' as Dr. Gurland calls it, may be the only means of communication. When victims are unaware of their bizarre behavior, relatives use cues to alert or distract them. They may sing, for example, as the wife did in the diner.
For the family, personality changes caused by stroke may be harder to bear than physical disabilities. In the weeks or months after a stroke, the patient may be irritable, demanding, self-centered. Unexplained bursts of crying or laughing are common. So are periods of depression, apathy and rage. While these symptoms generally disappear in time, they take their toll on the family.
Though no statistics are available on divorce among stroke victims, Mr. Chwat said the rate in families studied at Brooklyn College seemed ''high.'' Pat Singer, whose husband suffered a stroke four years ago, agreed. ''That's why we come to the stroke club,'' she said. ''You could break up your marriage very easily or put your mate away in a nursing home very easily.''
Mrs. Singer and her husband, Sam, who walks with a cane and a brace and who speaks few words, have undergone what the stroke club calls ''remaritalization.'' ''You have to understand you're not married to the same guy,'' she said. ''With speech therapy and physical therapy, they do get better, but not like before. My husband was a very macho man. He was the boss in our house. Now, I'm the boss, the mother, the everything.''
In some ways, the Singers are closer now than before. Baseball, for one thing, brings them together. ''I was never interested in sports before,'' Mrs. Singer said. ''Now I watch the games on TV with him and I make sure I know what teams are winning. I'll be part of his world. He can't be part of mine.'' Georgia Dullea