For three days and three cold nights this week, Margaret Henry, 62, huddled in the back seat of her family car off an isolated Prince George's County road, while her 75-year-old husband stalked the vehicle, refusing to let her leave.

From late Monday, when their 1972 Pontiac skidded off the isolated country road into a deep ravine, until Thursday afternoon, James Francis Henry held his wife prisoner there, immune to her entreaties that he go for help, beating her when she tried to leave, as he struggled with an acute mental breakdown.

The couples ordeal ended only when a passing bicyclist, hearing her voice, peered over the side of the road that winds past farms, churches and an occasional home, spotted the car in which James Henry had locked himself and his wife, and called the police. The cyclist departed without identifying himself and the two were soon taken by police to Prince George's General Hospital. Both were suffering from severe dehydration and strain.

Yesterday, James Henry was still in the midst of his emotional fog that hospital authorities has tentatively labeled "senile dementia." Several hospital floors removed from him, Margaret Henry recounted her tale of the three days and nights which she thought would be her last.

Their story began just after noon on Monday when the two drove over the dirt road that leads from their home, a dilapidated sharecropper house in the middle of one of the many tobacco fields that dominate the southern Prince George's landscape. The two had lived there for 20 years or more helping to harvest tobacco in exchange for free rent.

James Henry was driving that day, a duty he had recently turned over to his wife because he had, in her words, been acting "strange" and was unable to hold rational conversations. But because she had not been feeling well lately -- her older son had died the week before of a heart attack and her husband had been acting belligerent and refusing to take medication for his high blood pressure -- Margaret Henry was in no mood to argue when her husband insisted on driving.

They were going to see a relative who had attended their son's funeral, but for some unexplained reason the couple was unable to find the correct house and decided after an hour or so to return home to Mitchellville. As they traveled across Woodmore Road just a few miles from home, their 1972 Pontiac skidded off the road and down into a wooded ravine.

When the car came to rest, they were hidden from sight and the passenger side of the car was wedged against the underbrush, according to Margaret Henry.

"I said: 'What's happening, how we gonna get back up there?' and he said, 'I don't care.'" When she tried to get out of the car, her husband pocketed the keys and told her she wasn't going anywhere.

"He wouldn't let me out so after a while I climbed into the back seat and lay down there," she said. "I knew his mind's gone bad but I was trying to make out with him."

The next few hours were uneventful and as it grew dark Margaret Henry began to fall asleep. Suddenly her husband jumped into the back seat and "from nowhere he started stomping me, beating me with his workboots, jumping on my knees and he hunched me in the chest with his elbows," she said.

This went on for most of the night, she said. All the while Margaret cried out, "Don't do that. If you thump me like that I'm going to die." Her husband, she recalled, seemed unaware of what he was doing. Once he told her "I ain't hurt you, you old boy you."

When her husband finally stopped hitting her and began pacing around the car and up to the roadside, Margaret Henry found she was so sore it was difficult to move, her knees so bruised that she would have been unable to walk even if she had escaped from the car.

Throughout the beating, Margaret Henry had not noticed how cold it had become, a fact she would not be able to avoid in the coming nights.

Henry did not strike his wife again during their ordeal but he did not have to. His wife said yesterday she was to scared and sore to attempt an escape.

For the next two days and nights he paced around the car, refusing her request for food and water, ignoring cars and trucks that went by, apparently surrounded by his own emotional wilderness.

On Thursday afternoon, while the two of them sat locked in the car with the windows rolled up, Margaret Henry looked up toward the road and saw a young man on a bicycle peering through the bushes and the trees at her.

The man rode down to the car and knokced on the window saying, '"Are you all right?' I said, 'No, come and get us.'" But her husband refused to unlock the door to give up the key saying only "What difference does it make?" according to Margaret Henry.

Unable to get into the car, the bicyclist left for help, and, according to police reports, knocked on the door of a nearby house and told the occupants to call the police. The cyclist's identity is unknown. After directing police to the scene he pedaled up the road.

As Margaret Henry recalled it yesterday, within a few minutes of the bicyclist's departure, "there were people all over coming down that bank. They let me out but my husband said. 'Leave me alone, I want to stay here.'"

County police officers took the couple to a nearby medical facility and after a preliminary examination they were moved to Prince George's General where both were treated for severe dehydration.

Yesterday hospital authorities said Margaret Henry was recovering well and could be released today or tomorrow.

Her husband is being kept under psychiatric observation. According to Dr. Henry Wise Jr., their personal physician for the past 25 years, James Francis Henry had "shown evidence of mental deterioration for several years but until this time he had been able to cope. Apparently he just had a complete break."