John Keitz, 39, the vastly overweight Dundalk, Md., man who last spring began a physical therapy program, vowing to walk again after his extreme bulk had made him a prisoner of his bed for seven years, died yesterday of complications from an infection in a hospital in Youngstown, Ohio, his wife said.

Charismatic, funny, pugnacious, at times irascible, Keitz used his outsize personality to make friends and partially compensate for his otherwise restricted existence. He cooked and served chicken meals from his bed, played chess with neighborhood kids, "danced" to rock music by heaving from side to side and used the telephone to stay connected with the outside world.

His wife, Gina, was at his bedside, as she had been steadfastly since he first "went down" while making the couple a dinner of macaroni and cheese in the summer of 1998, when he weighed about 500 pounds.

Keitz's struggle, profiled in The Washington Post on June 26, provided a glimpse into the brutal and baffling physical and psychological hurdles involved in losing weight. He could not lie on his back because his chest bulk would suffocate him. He long refused to seek help, until, he feared, it might have been too late.

Yet with characteristic bravado, he said: "Don't underestimate the fat man."

He was optimistic about his prospects to the end. In a telephone interview Sept. 7 from a nursing facility specializing in obesity in Andover, Ohio, he reported that he was sticking to an 1,800-calorie diet and keeping up with his therapy.

"When I'm through I should be a lot leaner and more intimidating," he said.

The last 2 1/2 months were an uneven journey of progress and setback, like most of his life dealing with his weight.

June was a high point after a profound low. He had recently been evicted from his boyhood home, rendered homeless with Gina and his mentally handicapped sister, Jessie. The three lived on about $1,670 in disability checks and food stamps. Keitz entered Genesis Knollwood Manor in Millersville, a nursing home northwest of Annapolis specializing in obesity, paid for by Medicare and Medicaid, and with assistance from his therapist, he sat up -- for the first time in nearly three years.

Later in the summer, however, he started to feel sick and weak. He complained of breathing problems. Knollwood's administrator, Jeanne Marie Albanese, said yesterday that Keitz hadn't been complying with his diet. He was admitted to Baltimore Washington Medical Center with suspected pneumonia. Then Knollwood refused to take him back.

Albanese said yesterday that in the difficult process of moving Keitz to the hospital, the company realized it wasn't equipped to handle someone that heavy after all, should fire or another emergency require immediate evacuation.

But Keitz had learned of what he thought would be a better program for him at Andover Village Retirement Community, which specializes in people weighing up to 1,000 pounds.

When he entered Andover in late August, his weight had reached 752. In less than two weeks he lost 12 pounds. "The therapy here is unreal," he said Sept. 7. "They plan on having me upright real soon."

"He was being successful during his time here with weight loss," said Karyn French, director of social services at Andover. "He was saying he expected to be here two years. He wanted to lose weight and become functional, and that would be realistic" in two years.

Suddenly last week, his health declined dramatically. He was admitted Saturday to St. Elizabeth Health Center with a bacterial infection of undetermined origins that was attacking his organs, said Gina Keitz, 38. He was put on a respirator and a dialysis machine, and his heart would not pump without assistance, she said. It gave out yesterday morning.

A hospital spokeswoman declined to release details. But it is well known that extremely obese people live in a perpetual state of precarious health. The old term for those in Keitz's weight category is no longer politically correct but it may be accurate: "morbidly obese."

"The bodily functions and internal organs are not designed to carry the weight of what John was carrying," French said.

John Keitz grew up in Dundalk, the son of a steelworker at Baltimore's Sparrows Point. He was overweight as a child and became a fighter in response to playground taunting. He developed a lifelong love of cooking and worked in fast-food restaurants. He also briefly taught martial arts and sometimes settled disputes physically, claiming with some pride to have punched out a McDonald's manager who insulted him.

He said he tried any number of diets but came to the fatalistic belief that his body was incapable of losing weight. Some of his friends, however, said he did not heed warning signs and ate often, if not in great quantity at any one time.

"It was horrifying," Keitz said, looking back. "You just give up. You go, 'That's what I'm dealt with.' . . . You can only do what your body wants you to do."

After he became bedridden, one year melted into seven, as Gina sometimes worked more than one job at a time and the couple dealt with life on the edge of poverty and homelessness. Keitz made intermittent attempts to get therapy, but the sessions did not last. The abnormal became routine.

"He had a big heart and was trying to do what he could," Keitz's friend and former roommate Andy Gause said yesterday.

Keitz is also survived by four other sisters, from whom he was estranged, and a number of nieces and nephews.

His body will be cremated in Ohio, and Gina Keitz plans to bring his ashes back to the Baltimore area.

John Keitz celebrating his 39th birthday in June. He continued to gain weight until days before his death.