John W. Koons Sr., 59, a farm boy from Leesburg, Va., who became known as "King Koons, the world's largest Ford dealer," died of cardiac arrest Sunday at Holy cross Hospital in Fort Lauderdale, Fla.

Mr. Koons had been hospitalized March 5 for treatment of an aneurysm of the aorta, the major artery that carries blood from the heart.

If owning a car is part of the American dream, it was Mr. Koon's dream to own car dealerships. At this death, he presided over a corporation that operated a dozen family-owned automotive businesses in the Maryland and Virginia suburbs of Washington and in Annapolis.

Koons Ford at Seven Corners was the cornerstone of this corporate structure. It is said to be the largest retail Ford dealership in the United States and it is the reason he was called "King Koons." But his businesses, some of which are operated by his three sons, also sell Chevrolet, Pontiacs, Oldsmobiles, Toyotas, Jeeps and other vehicles.

In addition, there are the Koons Leasing Corp., the Koons Recreation Vehicle Corp., JK Auto Parts, JK Auto Distributors, as well as other companies. Mr. Koons also had extensive real estate interests.

He was a self-made man, and the obstacles he had to overcome were formidable. When Mr. Koons was 2, his father, John Edward Koons, died. The boy's mother, Donna Everhart Koons, moved from Philaelphia, where the family was living, to Leesburg, her hometown.

Young Koons grew up on a farm there. When he was about 18, he broke his neck in a swimming accident. The left side of his body remained paralyzed and he had to take treatment for the injury for the rest of his life.

A year after the accident, he went to work as a salesmen in a DeSotoPlymouth outlet in Falls Church. A year after that, he owned the place. He bought it for $350, part of which he had saved and part of which he borrowed from a school teacher named Eleanor Ayres, whom he latr married.

The year was 1941 and the nation's automobile industry was converting for the production of tanks, planes and other engines of war. But the late L.P. Steuarts, a Fall Church auto dealer, gave the young Koons some advice on how to make money in the automobile business even when it was clear that very shortly no automobiles would be available to sell.

He advised the young man to buy all the 1941 models he could lay his hands on and hang onto them. By 1943, these cars were of considerable value and Mr. Koons sold them and put the profits into real estate. When the war ended and car production resumed, he was ready with a new showroom that was located on his own land.

He opened DeSoto dealerships in other cities, foresaw the dmise of that car in the 1950s, got out of automobiles and into real estate, and then went back into cars. He opened Koons Ford in 1964.

"My motto in business is that I'm not a bit better than a carwasher, just more fortunate," he once said.

"You'll see morale out there," he said in an interview in his office off the Koons Ford showroom a year ago. "We build morale all the time...If anybody catches me out of my office with no smile and hits me on the shoulders, I give them $5.

"You know," he said, "nothing beats a smile."

According to salesmen and others who have worked for Mr. Koons, the injury he suffered in the swimming accident and the continuing therapy for it, may have made him a kinder man to work for than the average boss, with a strong sense for people and the pains and difficulties they suffered.

Those who have worked for him also depicted Mr. Koons as a hard driver, a positive thinker, a back slapper, and an enthusiast who would brook no negativism on the part of his staff. He wanted his dealerships to be the biggest and the best.

In manner, he was folksy, and gruff and gentle at once. He had wanted to be a doctor when he was a boy, but the paralysis resulting from his injury ended those plans.

"With the good Lord and a good wife, I managed to (come through)," he once said. "And the Lord blessed me with four good children . . . I'm very proud of them."

The children are John Jr., propretor of JKJ Chevrolet at Tysons Corner; James, who runs Koons Ford, and Joyce Koons Hish, whose husband, Art Hish, runs Koons Pontiac-Oldsmobile-Honda-GMC in Manassas, Va.

In addition to his business interests, Mr. Koons was active in church and community affairs. He contributed a car each year to the bazaar of St. James Parochial School and helped build Bishop Denis J. O'Connell High School in Arlington. He was chairman of the Easter Seal Drive in Northern Virginia for several years, was active in the Fairfax County Red Cross and in the United Givers Fund.

He was a director and then an honorary director of the the Boy Scouts of America, a member of the Falls Church Volunteer Fire Department, and a member and former trustee of the Fairfax Hospital Association. He was a member of St. James Church and of its parish advisory committee for the Catholic Diocese of Northern Virginia. He was a member of the Knights of Columbus.

Mr. Koons and his wife often vacationed in Florida. They traveled aboard a specially equipped bus because Mrs. Koons was not fond of flying. Mr. Koons also gave trips to groups of his employes on numerous occasions.

In addition to his wife, who resides at the home in Falls Church, and the four children, Mr. Koons is survived by a sister, Catherine Koons Adams, of Richmond.