Desi Arnaz, an actor, musician and producer and an important figure in the history of television, died yesterday of cancer at his home in Del Mar, Calif. He was 69 years old. With Lucille Ball, to whom he was married from 1940 until 1960, Mr. Arnaz created the situation comedy ''I Love Lucy.'' The program, which featured Mr. Arnaz and Miss Ball as Ricky and Lucy Ricardo, a Cuban band leader and his wacky, high-spirited wife, was produced from 1951 through 1956 and achieved unprecedented popularity.

Monday nights all across America, people would gather in front of what was usually the first television set in the house and watch the continuing adventures of Lucy and Ricky and their good-natured landlords and best friends, Fred and Ethel Mertz, portrayed by William Frawley and Vivian Vance. Lucy and Ethel were partners in comedic mischief; whenever Ricky became particularly exasperated, his broken English would degenerate into a torrent of Spanish epithets.

Now in syndication, ''I Love Lucy'' remains a staple of daytime television around the world, more than a quarter of a century after the last episode was filmed. ''A mad fan with insomnia, and some kind of yet-to-be-developed television receiver that can pull in any station on the air, could have his beloved Lucy on view almost 24 hours a day -if not in English, then in Greek, Portuguese or Bantu,'' Robert Metz wrote in his book ''CBS: Reflections in a Bloodshot Eye.'' Originated Idea of Reruns

The decision to film the program rather than perform it live made it possible to have high-quality prints instead of kinescopes, which were films taken off the television screen. Each episode could then be available for endless rebroadcasting. Unlike other shows of the era, ''I Love Lucy'' was filmed before a live audience, and used three cameras simultaneously to permit motion-picture-type editing. Reruns of ''I Love Lucy'' were shown during prime time for years after the show had ceased production. The appeal of reusable filmed programs led eventually to a seismic shift in television production from New York to Hollywood, and made the program's creators millionaires.

Mr. Arnaz and Miss Ball used the success of ''I Love Lucy'' to build a show-business empire, Desilu Productions. By 1957, Desilu owned a music-publishing firm, a record company, much California real estate and the Desi Arnaz Western Hills Hotel in Palm Springs (which advertised television sets in every room). The same year, the company purchased the four-block RKO-Radio Pictures plant in Hollywood and its sprawling subsidiary in Culver City, making Desilu the largest motion picture and television studio in the world.

By the early 1960's, however, Mr. Arnaz was increasingly unhappy in his marriage, and had developed a drinking problem. Desilu had become too complicated to handle in the direct, simple manner to which Mr. Arnaz was accustomed, and one of its hit series, ''The Untouchables,'' was under attack from members of the National Italian-American League to Combat Defamation because of its emphasis on characterizations depicting racketeers of Italian descent. 'Desi Wanted Out'

After a lengthy and publicized divorce, Miss Ball bought all of Mr. Arnaz's stock in Desilu for $3 million in 1962, and became the company's president. ''Desi has wanted out for a long time,'' Miss Ball said later in an interview. ''He's had the business bit. I honestly believe he enjoyed launching Desilu more than the actual running of it.''

''He was a great showman, a great business executive,'' she told the Ladies Home Journal in 1963. ''I was very proud of him. I still am. He built an empire. It was unfortunate that he also liked to let things fall apart. But there are a lot of people like that. They build and they destroy.''

Mr. Arnaz, christened Desiderio Alberto Arnaz y De Acha, was born in Santiago, Cuba, on March 2, 1917; his father was mayor of the city for nine years. After political turmoil drove the family to the United States, Mr. Arnaz began his career as a musician in New York and Miami, eventually leading his own band.

He first came to public attention in the 1939 Broadway production of ''Too Many Girls,'' which had a score by Rodgers and Hart and direction by George Abbott. ''As a South American broken-field runner, Desi Arnaz is a good wooer of women,'' Brooks Atkinson wrote in The New York Times. When the play was filmed by RKO-Radio Pictures the following year, Miss Ball was among the leading ladies; the two were married on Nov. 30, 1940. Each Had a Radio Series

Mr. Arnaz's films include ''Father Takes a Wife,'' ''Bataan'' and ''Holiday in Havana.'' By 1950, he had his own music series on the CBS radio network, while Miss Ball was appearing in the network's situation comedy ''My Favorite Husband.''

When the two in 1950 proposed what became ''I Love Lucy'' to CBS, they were met with two objections. First, CBS wanted the show broadcast live from New York, as was then the custom; second, some network executives thought that because of Mr. Arnaz's heavy accent, audiences would not find him credible in the role of Miss Ball's husband.

In the spring of 1951, to prove the network wrong, the couple went on tour, performing before live audiences across the country as a husband-and-wife comedy team. That summer, they produced a film pilot for the series with $5,000 of their own money. CBS, convinced, put the program on its fall roster on Monday nights from 9 to 9:30 E.S.T., but left all rights in the hands of the Arnazes. It was an immediate success; indeed, during its first six years, ''I Love Lucy'' never ranked lower than third in popularity among television programs. 'Discipline and Understanding'

''Fundamentally, it is a piece of hilarious theater put together with deceptively brilliant know-how,'' Jack Gould wrote in The Times in the show's early days, ''but it also is many other things. 'I Love Lucy' has no monopoly on the humor inherent in marriage; the idea is as old as the theater itself and television channels are cluttered with rival shows rather pathetically hoping that the 'Lucy lightning' will strike. But what seems to escape most of these imitations is the extraordinary discipline and intuitive understanding of farce that gives 'I Love Lucy' its engaging lilt and lift.''

It was a national occasion when Lucy Ricardo was seen going to the hospital to give birth to ''Little Ricky'' in the episode of Jan. 19, 1953 - the same night that Lucille Ball gave birth to her second child, Desiderio Alberto Arnaz 4th, in a Hollywood hospital. An estimated 44 million viewers - more than watched the inauguration of President Eisenhower the same month - tuned in to ''I Love Lucy'' for the event.

After leaving Desilu, Mr. Arnaz retired to his horse ranch near Del Mar. He continued to take an interest in show business, but mainly as what his daughter, the actress Lucie Arnaz, called ''a behind-the-scenes guy.'' He created pilots for several different series; one of them, ''The Mothers-in-Law,'' which starred Eve Arden and Kaye Ballard and attempted to capture some of the screwball atmosphere of ''I Love Lucy,'' ran on NBC from 1967 through 1969.

Rumors of serious illness had been circulating since Mr. Arnaz was hospitalized for diverticulitis in 1981. ''We all have been praying for two or three months that Desi would be released from his pain,'' Miss Ball said yesterday. ''Our prayers have been answered.''

Mr. Arnaz is survived by his wife, the former Edith Mack Hirsch; his daughter, Lucie, and his son, Desi Jr. Funeral arrangements will be private.