Mario Puzo, 78, whose romanticized portrait of the Mafia, "The Godfather," established a genre of popular literature and was the basis for Academy Award-winning movies now considered classics, died July 1 at his home in Bay Shore, N.Y.

The cause of death was reported as heart failure. He had had a quadruple bypass operation some years ago.

Mr. Puzo, the son of illiterate Italian immigrants, was the author of eight novels, starting with "The Dark Arena" in 1955 and ending with a book he had just completed, "Omerta," scheduled to be published in a year. "The Godfather," published 30 years ago, sold 21 million copies, and several of his other books were also bestsellers.

"Godfather," much imitated by other writers and said to be a source of fascination for genuine Mafiosi, was an epic story of the Corleone family of Sicily and New York. Mr. Puzo always said he had no actual firsthand knowledge about organized crime but had based his novels on research.

He also co-wrote eight screenplays. He won screenwriting Academy Awards for the first two of the "Godfather" trilogy, which were written with director Francis Ford Coppola and won best picture Academy Awards.

Among those starring in the movies were Marlon Brando, who won a best actor award, Al Pacino, Diane Keaton, James Caan, Robert Duvall and Robert De Niro, who won a best supporting actor award.

Mr. Puzo also worked on scripts for "Earthquake," two "Superman" movies, "The Cotton Club," "The Sicilian," "Christopher Columbus" and a television miniseries, "Mario Puzo's 'The Last Don.' "

Mr. Puzo was born in the Hell's Kitchen section of Manhattan. After serving in the Army during World War II, he studied at the New School of Social Research and Columbia University.

In a preface to a reissue of his early work two years ago, Mr. Puzo recalled the hardscrabble days following the commercial failure of the book he always considered his best, his autobiographical "The Fortunate Pilgrim." He felt he had failed his family by not making money from his novels.

Struggling to support his five children, he was working two jobs, as an adventure magazine writer and government clerk.

"I thought myself that most despised figure in Italian culture, a 'cooch'--that is, a man who could not earn a living for himself or his family.

"I decided to write a bestseller, and to use some stories that my mother--who is 'Pilgrim's' heroine, Lucia Santa--told us as we were growing up. That book was 'The Godfather.'

"It took me four years to write, still working two jobs. But it accomplished my aim. It was a bestseller, and this time I became rich and famous. I had done the right thing."

He always called "Godfather" a book about family rather than crime. The protagonist, Don Vito Corleone, had the courage and loyalty his own mother had shown, Mr. Puzo wrote. "His humanity came from her."

Vito Corleone, patriarch of his tight-knit clan, is an immigrant forced by circumstance into a life of crime. He comes to rule New York's rival gangster families with a kind of Machiavellian benevolence. When his antagonists rebuff him, he tells his underlings to "make them an offer they can't refuse."

His son Michael, a returning World War II hero, eventually comes to power. "Godfather" the movie stretched out into a three-part saga of capitalism, family, greed and treachery.

Mr. Puzo's other novels about the Mafia included "The Don," another flamboyantly sympathetic picture of mobsters, this time set in Hollywood.

"The success of Puzo's Mafia tales is rooted not in crime at all, but in the love of family," reviewer Roger L. Simon wrote of "The Don." "Even when family members act evilly to each other, ultimately we are to excuse them. Mafia family values are all. This allows us to enjoy acts that normally we would despise--one of the guilty pleasures of fiction."

In a 1996 Associated Press interview, Mr. Puzo acknowledged that his portrayals, with their emphasis on honor and family, made the Mafia a more romantic place than the thuggery or buffoonery of the real thing.

"They're not my Mafia," he said of the real-life mobsters. "My Mafia is a very romanticized myth."

He insisted that his research was done in libraries, not amid gangsters.

"Where would I have time to be in the Mafia?" he asked. "I starved before the success of 'The Godfather.' If I was in the Mafia, I would have made enough money so I wouldn't have to write."

And anyway, he asked, "Just because a guy's a murderer, he can't have endearing traits?"

Mr. Puzo's wife, Erika, died in 1978.

Survivors include his companion of 20 years, Carol Gino; five children; a sister; a brother; and nine grandchildren.

The Associated Press contributed to this report.

A WALK THROUGH THE PUZO LIBRARY

Books by Mario Puzo:

"The Dark Arena," 1955.

"The Fortunate Pilgrim," 1964.

"The Godfather," 1969.

"Fools Die," 1978.

"The Sicilian," 1984.

"The Fourth K," 1992.

"The Last Don," 1996.

"Omerta," due out July 2000.

Puzo's films:

"The Godfather," 1972.

"The Godfather, Part II," 1974.

"Earthquake," 1974.

"Superman: The Movie," 1978.

"Superman II," 1980.

"The Cotton Club," 1984.

"The Sicilian," 1987.

"Mario Puzo's The Fortunate Pilgrim," 1988, TV miniseries.

"The Godfather, Part III," 1990.

"Christopher Columbus: The Discovery," 1992.

"Mario Puzo's 'The Last Don,"' 1997, TV miniseries.

CAPTION: Mario Puzo's bestseller "The Godfather" was the leader in the genre he created.