Ray Kroc, 81, the founder, board chairman and impressario of the McDonald's hamburger empire who opened his first fast-food restaurant in Des Plaines, Ill., in 1955 and rode a set of golden arches into American legend, died yesterday at a hospital in San Diego. He had suffered a series of strokes and had diabetes.

Mr. Kroc was a prime example of the American dream. A native of Chicago and a high school dropout who lied about his age to serve in the Red Cross ambulance corps during World War I, he made a success of himself by hustling in the Chicago business world, where he led a radio orchestra, and selling paper cups. He later dabbled in Florida real estate.

Yet, his real journey to fame and fortune began in 1937, when he obtained the exclusive rights to the Prince Castle Multimixer, a contraption that could make up to six milkshakes at once. In 1954, his interest was piqued by an order for eight of the machines by one restaurant in San Bernardino, Calif.

He made the trek to the establishment, where he found Richard and Maurice McDonald, operators of a clean, well-lighted place, topped by a pair of golden arches. Outside, Mr. Kroc later said, were hundreds of people clamoring for hamburgers and milkshakes. He persuaded the brothers to let him merchandise their operation nationwide in return for royalties.

On April 15, 1955, he opened in Des Plaines the first "McDonald's" not run by the brothers. In 1961, he bought out their interest for $2.7 million, borrowing the money at interest rates that eventually cost him $14 million.

"I needed the name," Mr. Kroc explained. "How far could I go merchandising 'Kroc's' hamburgers? I needed that McDonald name."

The McDonald's business grew. By 1983, more than 7,500 restaurants displayed the golden arches in 32 nations in North America, Australia, Asia and Europe. The chain had sales of more than $8 billion last year.

Another measure of McDonald's success was that Mr. Kroc's bookkeeper took her pay in stock rather than in cash in the early days. When she retired that stock was worth $70 million.

What was the secret of his success? Perhaps it was his unique view of his calling. In his autobiograhy, "Grinding It Out," he wrote: "It requires a certain kind of mind to see beauty in a hamburger bun. Yet is it any more unusual to find grace in the texture and softly curved silhouette of a bun than to reflect lovingly on . . . the arrangement of textures and colors in a butterfly's wing?"

Perhaps the age was made for McDonald's. With America taking to the roads, a clean, inexpensive restaurant featuring hamburgers, fries and milkshakes may have been just what the doctor ordered. We deserved a break and wanted it all done for us. If he revolutionized American eating by founding the nationwide fast-food chain, his methods also were revolutionary.

He decreed that his concerns would not contain pay phones, cigarette machines or juke boxes, thereby discouraging them from becoming hangouts for teens and encouraging quick turnaround time in sales. They would carry a small menu, fill your order quickly and fly the American flag as often and long as possible.

Little was left to chance. Every modern research tool was used to determine just where restaurants would open. In the early days, this included Mr. Kroc's flying overhead in a light plane, counting church steeples and traffic intersections and studying traffic patterns to find the best location.

Before anyone was able to buy a McDonald's or to become a manager of a company-owned outlet, the person had to graduate from Mr. Kroc's Hamburger University in Elk Grove, Ill. The lucky graduates received a bachelor of hamburgerology with a minor in french fries.

A corporate manual spelled out just how each outlet should be run. The company formula of "quality, service and cleanliness" was upheld by surprise inspections by corporate employes. While the size and quality of the meat patties were uniform, catsup and mustard ratios varied according to regional tastes (more catsup, less mustard in the South, the reverse in New England).

The company also maintained sophisticated "trouble-shooters." It has been reported that in one Midwestern college town during the 1970s, students wanted the flag flown at half-staff the next day as part of a peace demonstration, while other groups told the local McDonald's manager, in no uncertain terms, that it better not fly at half-staff. The harried manager was told by a corporate trouble-shooter not to worry. Late that afternoon, a truck dispatched by the company "accidentally" knocked over the flagpole.

If he was a stunning success with McDonald's, Mr. Kroc met with less success, if with nearly equal fame, as owner of the hapless San Diego Padres baseball team. He bought the club in 1974 for a reported $12 million. He later explained he did it "because I needed a hobby."

Yet despite the infusion of more millions and the purchase of such free agents as Rollie Fingers, Gene Tenace, Oscar Gamble, Sal Bando and Steve Garvey, the franchise never finished higher than fourth. Not even the San Diego Chicken could help.

In a famous outburst in 1974, Mr. Kroc took the public address microphone at Padre Stadium and told a crowd of 40,000, "I've never seen such stupid ballplaying in my life." San Diego players, club officials and newspapermen criticized him for having "spoiled the night" and embarrassed the city.

Five years later, baseball commissioner Bowie Kuhn fined him $100,000 for announcing that he was going to go after yet more free agents. Mr. Kroc paid the fine and said, "Baseball can go to hell."

He once explained he found baseball to be like his wife: a lot of fun but no profit.

His first marriage ended in divorce. Survivors include his wife, Joan; a stepdaughter, Linda Smith; a brother, Dr. Robert Kroc; a sister, Lorraine Groh; and four grandchildren.